This PDF file contains the front matter associated with SPIE Proceedings Volume 7854, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The spectra obtained from Terahertz (THz) reflection imaging can be distorted by scattering from rough interfaces, layers, and granular inclusions. Since the facets of the object being imaged are not generally aligned normal to the THz beam, the received signal is produced from diffuse scattering, which can be appreciably lower in signal strength than specular returns. These challenges can be addressed with advanced signal processing approaches based upon the coherent and incoherent combination of returns from multiple sensors and frequencies. This paper presents two examples of physics-based processing strategies applied to THz imaging spectroscopy. The first method is based on synthetic aperture processing of a 2D sensor array to provide variable depth focused images of buried inclusions (a ball bearing embedded in polyethylene sample). The second method uses correlation processing to coherently combine multiple sensors and multiple frequencies to extract material signatures from measurements of THz scattering from rough interfaces. Results for both methods show an increase in performance relative to conventional imaging or spectroscopy approaches.

Terahertz(THz) transmission can be divided into passive transmission and active transmission, passive transmission refers to atmospheric propagation, active transmission means not only transmission but also completing a function, so also can be said functional transmission.Knowledge of the transmission of terahertz wave is very important for terahertz technology and its applications. We analysis detailed the atmospheric propagation model of terahertz wave, propagation effects, propagation equation, then carry out atmospheric propagation measurement system based on THz-TDS.

The THz-Infra-UV transmission spectra of Bi4Ge3O12 (BGO) and BGO:Ca, BGO:Pb crystals have been measured at the room temperature. The forbidden gap Eg of electronic energy bands are about 3.66eV (339nm). The quantities of adulteration Ca²⁺ and Pb²⁺ were very little (0.02 wt %), it did not influence Eg and the breadth of phonon absorption. The high frequency edge of the phonon absorption of the crystals was at 1700cm-1 (or 51THz). The low frequency edge of the phonon absorption was at 66 cm^-1 (or 1.98THz). Below 2.00THz the transmission T(1/λ) largened, maybe a nice transmission would be below 2.00THz in the three samples. The influence to the transmission from impurity Ca2+ ion was smaller than 10%, and from impurity Pb2+ion was smaller than 5%. Below 2.00THz the transmission T(1/λ) largened in the three samples.

The significant scientific and technological potential of terahertz (THz) wave sensing and imaging has been attracted considerable attention within many fields of research. However, the development of remote, broadband THz wave sensing technology is lagging behind the compelling needs that exist in the areas of astronomy, global environmental monitoring, and homeland security. This is due to the challenge posed by high absorption of ambient moisture in the THz range. Although various time-domain THz detection techniques have recently been demonstrated, the requirement for an on-site bias or forward collection of the optical signal inevitably prohibits their applications for remote sensing. The objective of this paper is to report updated THz air-plasma technology to meet this great challenge of remote sensing. A focused optical pulse (mJ pulse energy and femtosecond pulse duration) in gas creates a plasma, which can serve to generate intense, broadband, and directional THz waves in the far field.

The method of THz spectrum dynamics analysis (SDA - Spectral dynamics analysis - method) is applied for the detection and identification of substances by using the signal reflected from sample. It allows to obtain the spectrogram - composite Fourier spectrum dynamics - of the signal and to analyze the dynamics of many spectral lines simultaneously, even if the measurements are made on short time interval (less than 50 ps). The efficiency of the SDA method used for longer time intervals (more than 100 ps) is discussed also. The Fourier-Gabor sliding window method is used for obtaining the spectrogram. We consider the examples of finding the pure RDX and harmless materials (L-Tartaric Acid, Sucrose, PTFE) or their mixture in pellets by using a THz pulse reflected from them. A THz pulse with a few cycles falls on the sample and reflects from it. The receiver makes the discrete measurements of electric field strength of signal reflected from the sample. To restore the signal to the required accuracy the SVD - Single Value Decomposition - technique is used. Our investigations show that the spectrograms and dynamics of several spectral lines of the THz pulse reflected differ from the corresponding spectrograms and dynamics of spectral lines for the reference pulse under certain conditions and hence it is possible to detect the presence of the material in the sample of interest. The comparison of the Fourier spectrum of the substance with the corresponding spectrum calculated on the base of using an autocorrelation function for obtaining the spectrum shows that the AC-spectrum gives us essential less information about substance. From our consideration follows that in some cases the analysis of reflected signal on the short time interval (less than 50 ps) is insufficient for the reliable identification. It is necessary to analyze the response on the long time interval (about 300 - 400 ps). The analysis of spectrogram and spectral lines dynamics on the long time intervals gives the additional information about registering sub-pulses, which are appeared due to multi-reflection of THz wave from the boundaries of sample and from the reflecting elements of set-up, and relaxation times of excited energy levels of molecules. Hence, the reliability of identification increases.

Engine oil, most of which is extracted from petroleum, consist of complex mixtures of hydrocarbons of molecular weights in the range of 250-1000. Variable amounts of different additives are put into them to inhibit oxidation, improve the viscosity index, decrease the fluidity point and avoid foaming or settling of solid particles among others. Terahertz (THz) spectroscopy contains rich physical, chemical, and structural information of the materials. Most low-frequency vibrational and rotational spectra of many petrochemicals lie in this frequency range. In recent years, much attention has been paid to the THz spectroscopic studies of petroleum products. In this paper, the optical properties and spectroscopy of selected kinds of engine oil consisting of shell HELIX 10W-40, Mobilube GX 80W-90, GEELY ENGINE OIL SG 10W-30, SMA engine oil SG 5W-30, SMA engine oil SG 10W-30, SMA engine oil SG 75W-90 have been studied by the terahertz time-domain spectroscopy (THz-TDS) in the spectral range of 0.6-2.5 THz. Engine oil with different viscosities in the terahertz spectrum has certain regularity. In the THz-TDS, with the increase of viscosity, time delay is greater and with the increase of viscosity, refractive indexes also grow and their rank is extremely regular. The specific kinds of engine oil can be identified according to their different spectral features in the THz range. The THz-TDS technology has potentially significant impact on the engine oil analysis.

In this paper, the direct detection behaviors of a superconducting hot electron bolometer integrated with a log spiral antenna are investigated by using Fourier Transform Spectrometer (FTS). We find the response of the bolometer to a modulated signal can be detected by a lock-in amplifier not only from the DC bias current, but also from the output noise power at the IF port of the HEB. We attribute the response in output noise power to Johnson noise and thermal fluctuation noise. Both the current response and the output noise power response measured at different bias voltages can be explained by one dimensional distributed hot spot model. In addition, the frequency response of the hot electron bolometer measured from the response in DC bias current is in good agreement with that in IF output noise power.

Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. The spectral characteristics of Acesulfame-K in the range of 0.2-2.6THz had been measured with THz-TDS. We obtained its transmission spectrum, refractive index spectrum and absorption spectrum at room temperature in the nitrogen atmosphere. The results show that Acesulfame-K had the abnormal dispersions at 0.40THz, 0.66THz, 0.94THz, 1.79THz and 2.30THz. The vibration absorption spectrum of single molecule of Acesulfame-K is simulated based on the Density Functional Theory (DFT). It is found that Acesulfame-K has the obvious absorbance in THz region. This result shows that THz-TDS has a potential application in the field of food security.

The Dicke model was proposed by Dicke in 1954 to describe a single mode of photon coupled to an assembly of N atoms with the same strength. It was found that there is a quantum phase transition from a normal phase at weak coupling to a super-radiant phase at strong coupling at the thermodynamic limit N =∞. Here, we solve the model at N ≥ 1 and also discuss its possible experimental implementations inside a cavity. By studying the Dicke model by 1/N expansion, we identify an emergent quantum phase diffusion mode inside the super-radiant phase and also work out many remarkable experimental consequences of this mode such as its low frequency, photon number squeezing properties and photon statistics. The energy of the phase diffusion modecan be continuously tuned into many frequency ranges from Micro-wave to Terahertz (THz) to Infra-red. The photons from the super-radiant phase are in a number squeezed state with much enhanced signal/noise ratio which may have wide applications in quantum information processing. The photon statistics is strong sub-Poissonian. The effects of dissipations due to leaking photons out of the cavity are also discussed. The connections with the recent experiments of the strong coupling of a BEC of N ~ 10^{5 87}Rb atoms to the photons inside an ultrahigh-finess optical cavity are carefully analyzed. Several experimental schemes to detect the phase diffusion mode are proposed.

The efficiency of a simply designed optically pumped terahertz laser is studied experimentally. The terahertz laser cavity only consists of a quartz glass tube, an antireflection-coated Ge window and a SiO₂ window. The Ge crystal acts as the high-reflectivity mirror of terahertz radiation and the input coupler of pump laser instead of complicated metal-mesh mirrors. The Ge crystal is near 3 mm thick, whose exact thickness is designed according to etalon effects to maximize terahertz reflectivity. NH3 gas is filled in the cavity as the active medium and pumped by a TEA CO₂ laser. As high as 25.9 mJ terahertz radiation at the wavelength of 151.5 μm is extracted from 1.76 J pump energy. The corresponding photon conversion efficiency of this terahertz laser reaches 41.5%. A 4.7-mm-thick GaAs crystal and a 6-mm-thick ZnSe crystal are also chosen to be the input coupler. The experimental results show that the efficiency of the Ge window is 54% and 66% higher than that of the GaAs and ZnSe windows, respectively. The reason of the higher efficiency of the Ge window is demonstrated experimentally and theoretically in this paper.

An analytical solution of the optical susceptibility of quantum wells driven by a terahertz (THz) field is achieved based on the density-matrix formalism. A simplified three-level model is adopted for the quantum well structures, with the levels coupled by a near-infrared (NIR) and a THz field. The equation of motion for the polarization is derived from Liouville's equation for the density matrix. Using Floquet's theorem, and under the rotating-wave approximation with respect to the NIR probe field, analytical expression for the optical susceptibility of the driven quantum wells is obtained. Different features rising induced by the driving THz field in the absorption spectrum of the NIR probe are discussed for the THz field near resonance and out of resonance of the intraexcitonic transition. This analytical investigation of the susceptibility of the THz-field-driven quantum wells is much useful for clearly identifying the physical principles obscured in the full numerical calculations.

A Superconducting Integrated Receiver (SIR) comprises on one chip all elements needed for heterodyne detection: a low-noise SIS mixer with quasioptical antenna, a Flux-Flow Oscillator (FFO) acting as a Local Oscillator (LO) and a second SIS harmonic mixer (HM) for the FFO phase locking. Light weight and low power consumption combined with nearly quantum limited sensitivity and a wide tuning range of the FFO make SIR a perfect candidate for many practical applications. In particular, the SIR developed for novel balloon borne instrument TELIS (TErahertz and submillimeter LImb Sounder) covers frequency range 480 - 650 GHz. As a result of recent receiver's optimization the DSB noise temperature was measured as low as 120 K for the SIR with intermediate frequency (IF) band 4 - 8 GHz. The capability of the SIR for high resolution atmospheric spectroscopy has been successfully proven with scientific balloon flights from Kiruna, North Sweden. Diurnal cycles of ClO and BrO has been observed with BrO line level of only about 0.5 K. Possibility to use the SIRs for analysis of the breathed out air at medical survey has been demonstrated.

In this paper, square lattices of air holes were fabricated on a three-layer structure of metal-dielectric-metal using micromachining technology. The metal-dielectric-metal structure is based on RT/duroid 5870 produced by Rogers corporation. The square period is 400 μm and the radius of circular hole is 100 μm. The thickness of the structure is about 863 μm with metal thickness of 39.2 μm and dielectric layer thickness of 785 μm. The loss and dispersion of the dielectric layer with the dielectric constant of 2.33 are low at microwave frequencies. Terahertz transmission spectra through the sample were measured by the state-of-the-art THz-TDS system. Experimental results show that there is a transmittance centered at 1 THz with a wide pass-band exceeding 100 GHz. Transmission spectra calculated by FDTD method were given for comparisons and showed good agreements with the experimental results. Through analysis, the extraordinary transmission phenomena are caused by both the Febry-Parot effect and surface plasmon polaritons existing on the metal arrays.

More and more systems are requested to be more compact keeping constant system performances. One of the best approach is to reduce the pixel pitch of the IR detector while new technology improvements are carried out to improve the detector performance. The last developments at SOFRADIR / France for cooled IR detectors are following these trends. As a matter of fact, HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant improvements regarding their compactness, by reducing the pixel pitch, and regarding performances. Among the new detectors, the family of 15 μm pixel pitch detectors is offering a mid-TV format (384 x 288), a TV format (640 x 512) and a HD-TV format (1280 x 1024). The latest development concerning the mid-TV format is performed according to very challenging specifications regarding compactness and low power consumption. Thanks to recent improvements, the MCT technology allows to operate detectors at higher temperature (HOT detectors), in order to save power consumption at system level. In parallel, the 15μm pitch permits to reach challenging density and spatial resolution. This Focal Plane Arrays (FPA) is proposed in different tactical dewars, corresponding to various systems solutions.

A survey is made about the development of high frequency coaxial PTCs. The coolers cover from 30 K to 200 K and the cooling power levels from hundreds of milliwatts to 10's W. Tests suggest that they have the potential to provide appropriate cooling for HgCdTe-based infrared focal plane arrays from near visible down to very long wave infrared region. The paper also discusses the efforts to realize space qualified cryocooler technologies.

The uncooled infrared imaging based on MEMS has more and more broad space for development in recent years. An uncooled thermal detector array was designed and set up using bi-material micro-cantilever structures, which can bend with the temperature change. The effective image points of objects' infrared images which are read out by an optical method from this thermal detector array are discrete. For this reason, the output image should be filtered based on the gray mean value of square window, firstly. Then, each point of image can be decided to assign zero or restore the initial gray, according to the threshold of gray value summation of the filtered image's single direction template. Comprehensive two directions' data that is in horizontal and vertical, the final result is achieved. The experimental results demonstrate, this algorithm can remove noise well without losing the details of objects' effective image points.

Vibration disturbances generated by mechanical cryocooler, representing in a series of harmonics, are critical issue in practical application. A control system including electronic circuit and mechanical actuator has been developed to attenuate the vibration. The control algorithm executes as a series of adaptive narrowband notch filters to reduce corresponding harmonics. The algorithm does not require actuator transfer function, thus ensure it more adaptive. Using this algorithm, all the vibration harmonics of Cryocooler were attenuated by a factor of more than 36 dB, i.e., the residual vibration force was reduced from 3.44Nrms to 0.05Nrms over the 300 Hz control bandwidth, the converging time is only less than 20 seconds, and the power consumption of mechanical actuator is less than half a watt. The control system has achieved the general vibration requirement of Infrared application.

The area array three-dimensional (3D) active imaging laser radar is a kind of remote sensing system which benefits high detection speed. This type of laser radars employ area optical modulation devices such as micro-channels plate (MCP) image intensifiers to modulate the photons flying time into intensity which can be detected by a charge coupled device (CCD). The distance measurement precision of this kind of laser radars is determined by the short noise of the photons numbers. This property limits the performance of this kind of laser radar. In this paper, a method based on second-order coherence is presented to compensate the short noise. The analysis result shows the photon bunching effect improves the SNR of the distance measurement with the same photon numbers. The second-order coherence based method is proposed to prove the 3D active imaging laser radar SNR. An experiment system is introduced which has results verified the theory.

Pulsed thermography is a technique in which pulsed flash energy is applied to the surface and the temperature of the surface is recorded and analysed. Generally the temperature above the defect areas is different from that of the surrounding area. However, when the surface of the specimen is highly reflective, artifact of fixed pattern could be introduced which comes from the reflection of the heated lamp tube. Several methods were used to eliminate the artifact, including spatial filtering, image subtraction and frequency domain filtering. Results show that spatial filtering may be the best method of the fixed pattern artifact elimination.

On the basis of electromagnetic theory, the scattering light intensity from a series of dielectric surfaces with different roughness is calculated by using monte-carlo method and the boundary condition of Kirchhoff approximation. The geometry profile of rough surfaces obeys Guass distribution and all of the surfaces have the same corelation length. With the increasing of rms height, the width of diffuse scattering intensity distribution, the attenuation of scattering peak value and its moving to the normal direction are observed. After theoretical analysis, it is obtained that the statistical distribution of the local slope varies with the rms height and reflecting index of these local slope are the main reasons for these phenomenon.

The achievement of the Planck and Herschel space missions in the submillimeter and millimeter range was made possible by a continuous effort on detector developments. Now limited by the intrinsic fluctuations of the radiation coming from the astronomical sources themselves, the sensitivity improvement requires the development of large arrays of detectors filling the focal plane of the telescopes. We present here the development of a TES array using NbSi sensors on SiN membranes. The readout electronics is based on SQUIDs and a cooled SiGe ASIC multiplexer. The detector is coupled with the input radiation by means of antenna. The present goal performance is adapted for the realisation of a ground based millimeter camera.

The design and development of microbolometer passive infrared (PIR) security sensors at Electro-optic Sensor Design (EOSD) has previously been described at the present and other SPIE forums. The primary object of this patented technology is to provide a higher performance option to current pyroelectric PIR sensors, including longer detection range, detection of developing fire and machinery failure, and imaging capability. A number of other applications have been identified. The EOSD sensor technology employs a novel mosaic-pixel focal plane detector array (MP-FPA), together with purpose-designed optics and electronic readout to achieve high detective performance in low product cost, short range sensor applications. In previous papers emphasis was placed on FPA design for amorphous silicon (a-Si) microbolometers, and other materials were briefly discussed as options. In this paper new MP-FPA designs will be described for further performance enhancement and application to vanadium oxide (VOx) and other silicon alloys, including amorphous Si:Ge. The designs are intended for high volume production in CMOS/MEMS foundries. The performance of different FPA designs is compared for upgrade PIR security sensors and low cost thermal imagers.

In this paper, the terahertz transmission properties of metallic fractal structures are presented by the terahertz time domain spectroscopy and the numerical analysis based on the finite differential time domain simulation. Several metallic fractal structures including the H-shape fractal pattern and the square-hole fractal pattern are studied. The terahertz transmission spectra of these metallic fractal structures are shown at two polarization of terahertz field perpendicularly. The results show that the asymmetric metallic fractal structures such as H-shape fractal structure have an obvious polarization dependent and frequency selective transmission. The symmetric structures have no such polarization dependence. Terahertz transmission through the H-shape metallic fractal structure can be switched between the different pass bands by changing the polarization direction of terahertz field relative to the first-level fractal line. Therefore, a potential application may be to realize a polarization tunable terahertz filter based on this kind of H-shape metallic fractal structure.

Interrogation is an important step for seeking truth from the suspect. With the limit of the intrusive nature of the current polygraph, we show here a highly-sought-after non-intrusive lie detection system with a user-friendly interface called TAD². The key idea behind our TAD² is based on the analysis of far-infrared data obtained remotely from the periorbital and nostril areas of the suspect during the interrogation. In this way, measured change in skin temperature around two periorbital areas is converted to a relative blood flow velocity while a respiration pattern is simultaneously determined from the measured change in temperature around the nostril region. In addition, TAD² is embedded with our automatic baseline assignment that is used for distinguishing the subject's response into normal or abnormal stage. In our TAD², the officer can choose to perform one of the three standard lie detection tests, namely, a modified zone comparison test, a modified general question test, and an irrelevant & relevant test. Field test results from suspects in real crime cases are discussed.

Terahertz interferometry from high altitude site in Antarctica is proposed. Requirements for future terahertz astronomy are followed by comparison of interferometer technologies. Heterodyne interferometer can use matured technology and achieve high frequency resolution, whereas, direct detector interferometer can achieve observations in large bandwidth and wide field of view using focal plane arrays. As an example of direct detector interferometry multi-Fourier transform interferometer (MuFT) is introduced, which utilize Martin-Puplett type Fourier transform spectrometer, which is essential to realize multiplying interferometry to avoid atmospheric background fluctuation. As another example, photon counting interferometry is introduced. By implementing fast response FIR detectors to measure photon arrival time, visibility can be measured by the correlation of the photon statistics.

The phase assemblage and dielectric properties of (Ca_0.5+x Sr_0.5-x)[(Al_0.5Nb_0.5)_0.5Ti_0.5]O₃O3 ceramics (abbreviated as CSANT hereafter) in Terahertz waveband were investigated. The CSANT complex perovskite was unstable at Ca2+-rich composition, a secondary phase were easily segregated in x ≥-0.05 region. The main perovskite phase CSANT crystallized in Fm3m cubic symmetry in the composition range of x≤-0.1, however, it transited to Pbnm orthorhombic space group after x=-0.1 due to the antiphase tilting of oxygen octahedra. As x further increased to x=0.2, or the tolerance factor decreased to 0.9785, A-site Ca²⁺/Sr ²⁺ cations antiparallel displacements also appeared. The dielectric absorption property of CSANT ceramics in THz frequency range was investigated using time-domain transmission spectrum technology and was correlated to their microstructures. The compositional dependence of the power absorption property of CSANT ceramics exhibited a monotonous variation in 0.1~2.5THz frequency. A lowest THz power absorption ceramic could be obtained in CSANT compounds at x=0.3 when sintered at 1500°C for 4hrs.

We present terahertz time-domain spectroscopy characterization of human thumb skin in reflection measurement mode with waveform rebuilding technology. The thumb skin contacts one side of a high resistive silicon wafer with 3 mm thick, and here is an orthogonal incidence of the THz pulse putting on the other side of the wafer. We rebuild the time domain signal from silicon-skin interface as a sample signal by the signal from the air-silicon interface as a reference and a Fresnel transform function between them. Material parameters were calculated by minimizing the difference between the measured sample waveform and a rebuilt one in time domain. The double Debye model parameters for the thumb skin were fitted. The method has potential to research complex layer-structures in skin if a precise model is built.

Detection and identification performance prediction is an important part in designing the passive terahertz imaging system. This paper presents a novel detection and identification model of passive terahertz imaging system for concealed extended target. In the modeling process we take into account main factors such as radiation principle of target and background, the characteristics of atmospheric transmission, and imaging detecting system. Firstly we research interaction principle of terahertz radiation for object based radiation principle of low temperatures terahertz blackbody. We calculate target and background terahertz radiation power. So target-to-background contrast is described in different fields and ranges. Secondly, we research the effect of terahertz beam attenuation in atmospheric environment, and choose the best terahertz atmospheric absorption frequency. So we can account target radiation power in the surface of detector. Lastly we research passive terahertz imaging detecting method for improving THz radiometric resolution. Due to testing target is extended, the two dimensional real-time scanning method is adopted. So we account identification probability of passive terahertz imaging system in different distance. The paper shows results in different distances and is useful to design and evaluate the passive terahertz imaging system for concealed object detection and identification.

This paper describes a novel multi sensors image fusion technology which is presented for concealed weapon detection (CWD). It is known to all, because of the good transparency of the clothes at millimeter wave band, a millimeter wave radiometer can be used to image and distinguish concealed contraband beneath clothes, for example guns, knives, detonator and so on. As a result, we adopt the passive millimeter wave (PMMW) imaging technology for airport security. However, in consideration of the wavelength of millimeter wave and the single channel mechanical scanning, the millimeter wave image has law optical resolution, which can't meet the need of practical application. Therefore, visible image (VI), which has higher resolution, is proposed for the image fusion with the millimeter wave image to enhance the readability. Before the image fusion, a novel image pre-processing which specifics to the fusion of millimeter wave imaging and visible image is adopted. And in the process of image fusion, multi resolution analysis (MRA) based on Wavelet Transform (WT) is adopted. In this way, the experiment result shows that this method has advantages in concealed weapon detection and has practical significance.

The bit error ratio (BER) and power are very hard to calculate in space optical communications, having lots of effect factors, so need compromise to consider the complex factors. Analysis the influence to the BER such as beam drift, beam divergence angle, communication distance, link loss, detector sensitivity etc. Propose the view of ellipse gauss beam can inhibit beam drift by the random shock and relative motion of the optical platform and reduce the BER, and further propose the method of calculate the transmit power using the BER. Experiments showed that it is security to use the calculation methods of BER and power.

The low-frequency optical properties of CuS nanoparticles in the composite samples were measured by the terahertz time-domain spectroscopy. Then, the power absorption, refractive index, complex dielectric function and conductivity of pure CuS nanoparticles are extracted by applying Bruggeman effective medium theory. The measured dielectric function and conductivity are consistent with the Lorentz theory of dielectric response as well as the Drude-smith model of conductivity in the frequency range from 0.2 to 1.5 THz, respectively. In addition, the extrapolation of the measured data indicates that the absorption is dominated by the lattice vibration localized at 4.7 ± 0.2 THz and the time constant for the carrier scattering is only 64.3 fs due to increased electron interaction with interfaces and grain boundaries.

SrB₄O₇ (SBO) is a promising nonlinear optical crystal. It has the orthorhombic structure with group classified as Pnm2. The sample for the experiment was cut along the (001) plane and twin polishing with 1.632mm thickness. It exhibits a wider transparency range from UV to far-IR. And its absorption edge lies at 160nm. The forbidden band gap is about 7.76eV. The THz spectra of SBO crystal had been studied from 0.1 to 2.5THz. The THz time domain spectrum of SBO shows the strong resonance characters. In THz experiment, the vertical incident electromagnetic waves radiate the polished side twice along (001) orientation. The crystal turned 90 degrees relative to the first in the vertical direction. There are different optical properties in two directions. We gained the curves of the refractive index and absorption coefficient dependence of frequency in the region of 0.1-2.5THz. The absorption curves shows opposite parabola character. One is upward opening and the largest absorption coefficient is 10cm^-1. The other is down opening and the less absorption coefficient is 1cm^-1. The refractive index n is stable linear with frequency and it is 3 from 0.4THz to 2.5THz. But the refractive index of two directions shows the opposite tendency from 0.1 to 0.4THz. The reason of the difference is that polarized beam radiates the orthorhombic crystal. The properties of the sample show that it is possible to apply it to laser field.

The thin films of W-doped VOx, were synthesized onto glass substrates using reactive DC magnetic co-sputtering deposition technique. The optimum synthetic process was obtained when the gas pressure was 2.0Pa , the ratio of O2/Ar was 1.0:15, the sputtering powers were 120W for vanadium target and 45W for tungsten target during 30minutes, and all W-doped VOx films were annealed in nitrogen atmosphere at 450°C for 2 hours. The structures of films were characterized by X-ray diffraction. The effects of W dopant on the semiconductor to metal phase transition of bare VOx were investigated with measuring the dependence of electrical resistance on temperature and the infrared transmittance spectra. Remarkably strong effects of W doping were observed on VOx films both the optical and electrical properties. The IR transmittance was decreased from 67.46% to 44.86%, while the transition temperature from monoclinic semiconductor to tetragonal metal was decreased from 68°C to 48°C through W-doped. In addition to, the temperature coefficient of resistance was changed from -1.48 %/ °C into -1.71 %/ °C for W-doped VOx film at corresponding transition temperature.

Propagation of a continue THz wave in random coal aggregates are studied using generalized multisphere Mie theory and Monte Carlo(MC) simulation. Coal aggregates are obtained by the DLA model. Scattering characteristics of monomers and aggregates in coal clouds are analyzed by generalized multisphere Mie theory. For a single coal monomer and a coal aggregate, scattering intensities versus scattering angles are given. The effects of the radii of monomers on the scattering efficiency factors, extinction efficiency factors and absorption efficiency factors are computed and discussed. With the MC method, the transmission of a THz wave in a coal clouds layers is simulated.

Because of its unique nature, terahertz radiation has wide application prospects in physics, chemistry, biomedicine, communications, radar and security checks, etc. Liquid crystal, which is a kind of macromolecule soft material with special properties in physical and chemical, has been widely used in planar displays. Recently, much attention has been paid to non-display studies of liquid crystals, covering the fields of biology, chemistry, physics, material and engineering. In this paper, the transmission spectra of several nematic liquid crystals such as 5CB, TEB300, RDP-92975 are measured by THz time-domain spectroscopy technique and free-space electro-optic sampling method. The absorption coefficients of liquid crystals in the THz range are calculated. Furthermore, the optical parameters are compared and analyzed, expecting to fill the spectrum gap of liquid crystals in the THz range and provide the experimental and theoretical foundation for the application of liquid crystals.

The generation of terahertz (THz) wave from a single-color femtosecond (fs) laser-induced air plasma with a dc biased field is studied. A systemic investigations of the THz wave polarization by changing the direction of dc biased field in parallel or perpendicular to pump pulse polarization. The results demonstrate that the THz wave generation is the sum of ponderomotive force and the dc biased field, and the external dc biased field can amplify and modulate the total THz waveform.

We present a polarization-controlled terahertz (THz) wave spectroscopic imaging modality to investigate the anisotropy of the detected materials. The polarization of the emitted THz wave is controlled to be horizontal and vertical by changing the relative phase of the fundamental and second-harmonic waves in the two-color laser-induced air plasma THz generation configuration. The anisotropy of the industrial sprayed-on-foam-insulation (SOFI) is characterized by measuring its azimuthal angle dependent THz polarization response. This work demonstrated that THz wave polarization-controlled imaging technique can be used for highly sensitive industrial inspection and biological related characterization.

We built a reflective mode terahertz time domain spectroscopy system for sealed liquid detection. We used air plasma THz emitter for obtaining a high THz power of 5mW and used ZnTe electro-optic (EO) sampling for getting high sensitivity difference detection. Experiment demonstrates this system can detect the liquid in the sealed container. We measured the reflection data on the second interface between the sealed container and the inside liquid. The signals from the top interface show a relation with the refraction coefficients of the liquid in the THz region by using Fresnel's equations. The liquid can be indentified by comparing the curves of reflection and a database of known liquid refraction coefficients. In this paper, water, ethanol and ethylene glycol were detected and indentified. In additional, the data processing and analysis for getting the reflection data on the second interface are discussed.

To reduce weight and improve strength in the aerospace industry, composite structure has gained popularity as a replacement for conventional materials and structures, such as adhesive bonding and honeycomb structure. Honeycomb structures composed by a honeycomb core between two facesheets are very common on aerospace parts. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining methods. With the large increase in the use of composite materials and honeycomb structures, the need for high speed, large area inspection for fracture critical, sub-surface defects in aircraft, missiles and marine composites led to broad acceptance of infrared based NDT methods. Infrared thermography is one of several non-destructive testing techniques which can be used for defect detection in aircraft materials. Infrared thermography can be potentially useful, as it is quick, real time, non-contact and can examine over a relatively large area in one inspection procedure. In this paper, two kinds of defects which are of various size, shape and location below the test surface are planted in the honeycomb structure, they are all tested by pulsed thermography, analyze the thermal sequence and intensity graph got by this methods, it shows that pulsed thermography is an effective nondestructive technique for inspecting disbonding defect, can distinguish the location and the dimension of the defect exactly.

This paper describes a new detection technology related to the bolometric micromechanical sensor for detecting THz radiation. The micromechanical sensor comprises thermo-sensitive bi-material micro-cantilever, micro-prism and optical readout system based on surface plasmon resonance for detecting the bending of the micro-cantilever. In static mode, incident radiation absorption raises the temperature of cantilever and, as a result, it bends proportionally. The cantilever bending changes the thicknesses of the gap between the lower surface of the cantilever and the metallic thin film. It will result in a shift of the SPR angle. Consequently, the surface plasmon excitation efficiency and therewith the measured at a fixed incident angle reflectance of a metallic film will be changed almost proportionally to the cantilever bending. Therefore the incident radiation power can be determined via the metallic film reflectivity change. The paper introduces the bi-material for fabricating the micro-cantilever and the optimal thickness of the gold film which is obtained through computer simulation. The material of silicon is used to fabricate the micro-prism, and the technique procedure for manufacturing the micro-prism and the micro-cantilever is described in detail. Because of its uncooled performance of the detection technology, the micromechanical sensor will have a low cost and be easy for fabrication of large bi-dimensional arrays.

According to the configuration and technical specification of the detector, which has multiple channels, channels mixing, high speed outputs and separate columns between odd and even, a real time digital processing unit based on the CPLD, FPGA and DSP has been developed to achieve the data synthesis and arrangement function and the parity correction algorithm. A special interface circuit with 4 CPLDs is designed to complete the first synthesis step where the 16 channels of data are combined into 4 channels. The second step is finished in FPGA and ROM address encoder where the 4 channels of data are combined into 1 channel. For output data synchronization, FIFO is adopted to achieve the delay of even channels in the parity correction. Data of odd channels enters the columns synthesis unit without any processing and even channels shall be processed in the columns synthesis unit after entering the FIFO unit first and experiencing the delay process. Thereby the pre-processing before image processing of the linear array thermal imager is accomplished.

The energy of solar radiation on the earth mainly concentrates in 0.29~3μm wavelength range, where infrared wave accounts for 53 percent, visible light accounts for 44% and ultraviolet accounts for 3%. For the photovoltaic cells, different light coming from solar radiation has different energy and different penetration depth. For the short waves, the photovoltaic cells have large absorption coefficient and have small absorption coefficient for the long waves. As for the sunlight, if the photon energy is greater than the semiconductor forbidden bandwidth, it will inspire electron-hole pairs, and vice versa. When the range of wavelength is 0.5~1.2μm, silicon photovoltaic cells can transform the light energy into electrical energy and heat energy, and only heat energy to the light which wavelength is greater than 1.2μm. So, the photovoltaic cells will make most of the sunlight change into heat energy, which will influence the characteristics of the photovoltaic cells unless the heat was dissipated in time. In the paper, the thermal battery pasted on the back of the photovoltaic cells is adopted to absorb the heat, so the photovoltaic cells can keep a good state long time. The strategy of energy management is presented in the paper in detail.

Due to the development of IR FPAs resolution and the transmission speed of the images, the requirement for the high speed IR images transmission becomes a significant part in the whole IR imaging system. The fiber based transmission method is proved to be a promising technique which can replace the traditional methods based on the electrical signals. This paper introduces the design of digital IR images transmission technique based on fiber, according to the characteristics of IR imaging data. This long wire transmission is accomplished utilizing the FPGA which is designed to control the data cushion synthesis process, receive the high speed imaging data and send out the real time VGA images. FPGA provides the reference clock signals to help the encoder convert the 16 bits parallel imaging data into the serial LVDS signals. Then the MAX9376 chip is introduced to convert the LVDS signals into the LVPECL signals, for only the LVPECL signals can be received by the laser diode. The receiving process is just opposite, where the LVPECL signals are finally converted into the parallel data. To verify this design, the VGA controller function is achieved by Verilog HDL programming in FPGA, so that the parallel IR imaging data can be converted into the high resolution images. The experiment images show that the effective resolution of the image in 64Mhz is 1024×800, and the transmission rate reaches 1.125Gb/s which is much higher than the traditional methods and fully satisfies the requirement for the long distance IR imaging data transmission.

The FPA Infrared imaging technology is widely used in military and civilian fields, and the optical readout FPA Infrared imaging technology is one of the most important branch. How to get a higher sensitivity IR image is very important since there are many factories that can degrade image quality. In this paper we introduce a method to improve system image quality, which is called the holographic compensate illumination based on the holographic technology. Firstly, we analyze the key influencing factors of the image quality of an optical readout FPA IR imaging system, and the two kinds of manufacturing errors of the FPA are given. Then we point out the principle of the method to compensate the FPA fabrication errors and design the experimental scheme. The result of the experiment shows that we can get a more uniform and higher sensitivity IR image by the method of holographic compensate illumination.

The traditional least mean square (LMS) algorithm has the performance of good adaptivity to noise, but there are several disadvantages in the traditional LMS algorithm, such as the defect in desired value of pending pixels, undetermined original coefficients, which result in slow convergence speed and long convergence period. Method to solve the desired value of pending pixel has improved based on these problems, also, the correction gain and offset coefficients worked out by the method of two-point temperature non-uniformity correction (NUC) as the original coefficients, which has improved the convergence speed. The simulation with real infrared images has proved that the new LMS algorithm has the advantages of better correction effect. Finally, the algorithm is implemented on the hardware structure of FPGA+DSP.

This research indicated the experiment method to analyze and predict the effect of turbulence on the performance of IR thermal imagers. First, the values of structure constant of refractive index, C_n ², were measured. The C_n ² model used in engineering applications is also introduced. And the calculated values were compared to the experiment data, so that the model can be modified. Meanwhile, two IR thermal imagers in MWIR and LWIR bands were installed to provide the data on the range performance. After that, the range values as a function of varying turbulence were calculated utilizing the simulation tool. Finally, this paper analyzed the range values in different groups.

This paper describes a new opto-mechanical scanner that is hopeful for terahertz imaging in security applications. The target of using this scanner is portal screening of personnel for high-resolution imaging of concealed threat objects. It is not only applied to active terahertz imaging but also applied to passive Terahertz imaging. Terahertz wave can penetrate many materials that are opaque to visible and infrared light, such as plastics, cardboard, textiles and so on. So the terahertz imaging technology has a potential to be applicable in security inspection at airports, stations and other public place. Now, the most terahertz imaging system works at point to point mechanical scan pattern. The speed of this raster scan is too slow to apply in practical field. 2-D terahertz array detector can be applied to real time imaging. But at present their cost is prohibitively high. Fortunately low cost, high performance, opto-mechanically scanner is able to meet the current requirements. An opto-mechanical scanner should be able to rapidly scan a 2-D image of the scene. It also should have high optical efficiency so that an image system can achieve the required thermal sensitivity with the minimum number of receivers. These ensure that it can easily operate at any wavelength, and be active or passive. The opto-mechanically scanning can meets these requirements and is being developed into a high performance, low-cost prototype system that will meet the future needs for terahertz security.

The azimuthal angle dependent transmittance in 0.2-2.2 THz frequency region for magnesium fluoride (MgF₂) crystal is measured by using a polarization sensitive detection method. The birefringence, absorption coefficient and refractive index have been studied. Based on the theory of crystal optics, the possibility of using magnesium fluoride (MgF₂) crystal as a THz wave plate is investigated. The coincidence of experimental data and theoretical curve demonstrates that these optical properties are sufficient for being used as wave plate operating in 0.2-2.2 THz frequency region.

The polarization information of various ores and gems in the terahertz (THz) frequency region has been investigated. The images of the samples for different polarization are captured by a balanced polarization imaging system. The system employs a balanced electro-optic (EO) detection method for two-dimensional THz real-time imaging, which systemically integrates the THz balanced EO sampling technique and the dynamic subtraction technique. The proposed method can effectively improve the signal to noise ratio and the spectrum measurement accuracy of the imaging system. The imaging speed is dramatically reduced by using two high speed CCDs which are used to detect two orthogonal polarization components of probe beam. The subtraction of two corresponding images presents the balanced image of the sample. By rotating the polarization of the probe beam by 45 degree, another polarization component which is orthogonal to the present one can be measured. The experiment results demonstrate the advantage of the method. The spectra of the samples on each point can be extracted from a series of images, thus the refractive indices, absorption coefficients, and polarization rotation coefficient can be drawn. The information can be used to identify samples.

Computational unified device architecture (CUDA) is used for paralleling the spectral scattering calculation from non-Lambertian object of sky and earth background irradiation. The bidirectional reflectance distribution function (BRDF) of five parameter model is utilized in object surface element scattering calculation. The calculation process is partitioned into many threads running in GPU kernel and each thread computes a visible surface element infrared spectral scattering intensity in a specific incident direction, all visible surface elements' intensity are weighted and averaged to obtain the object surface scattering intensity. The comparison of results of the CPU calculation and CUDA parallel calculation of a cylinder shows that the CUDA parallel calculation speed improves more than two hundred times in meeting the accuracy, with a high engineering value.

Vanadium oxide thin films fabricated by reactive magnetron sputtering were annealed in N2/H2 ambience for 1, 3, 5 and 7 hours at 450°C. Changes in electrical & structural properties and chemical composition were studied. From R-T measurement and calculation, it was found that both square resistance(R) and temperature coefficient of resistance(TCR) of the films increased after annealing. Atomic force microscopy(AFM) analysis revealed that both grain size and surface roughness were aggrandized greatly after annealing. X-ray diffraction(XRD) analysis showed that new phases V₂O₅(0 0 1) and VO₂(0 1 1) appeared in the annealed films and the grain size varied between 10~40nm. X-ray photo-electronic spectrum(XPS) analysis demonstrated variations in depth of the atomic ratios of O:V and the vanadium valence states distribution for different time annealed films. Following the above analysis, correlation between macroscopic and microscopic characteristics of the films is elaborated.

Our purpose is to realize a multi-pixel sub-millimeter/terahertz camera with the superconductor - insulator - superconductor photon detectors. These detectors must be cooled below 1 K. Since these detectors have high impedance, signal amplifiers of each pixel must be setting aside of them for precise signal readout. Therefore, it is desirable that the readout system work well even in cryogenic temperature. We selected the n-type GaAs JFETs as cryogenic circuit elements. From our previous studies, the n-type GaAs JFETs have good cryogenic properties even when those power dissipations are low. We have designed several kinds of integration circuits (ICs) and demonstrated their performance at cryogenic temperature. Contents of ICs are following; AC coupled trans-impedance amplifiers, voltage distributors for suppressing input offset voltage of AC coupled CTIAs, multiplexers with sample-and holds, and shift-registers for controlling multiplex timing. The power dissipation of each circuit is 0.5 to 3 micro watts per channel. We also have designed and manufactured 32-channel multi-chip-modules with these ICs. These modules can make 32- channel input photo current signals into one or two serial output voltage signal(s). Size of these is 40mm x 30mm x 2mm and estimated total power dissipation is around 400 micro watts.

Rigorous coupled-wave analysis is used to calculate the diffraction efficiency of THZ spectrum gratings. The ratios of grating periods and wavelengths and the ratios of grating depths and wavelengths of different type gratings are analyzed in this paper. Calculated results show that if the ratios of grating periods and wavelengths approximately equal to 1 and the grating depths greater than1.5, high diffractive efficiency of TE and TM polarization of symmetrical shape gratings will be got.

In infrared scanning imaging system, long linear-array detector is needed for large field of view. Instead of using long linear-array detector, we couple a non-conventional Infrared (IR) fiber bundle to a small scale Infrared Focal Plane Array (IRFPA) whose format is 320×256 in system to implement 1024×4 format linear array imaging. The input of fiber bundle is long linear array while output is plane-array. Fibers in IR fiber bundle are one to one mapping. Input end of fiber bundle is set at the focal plane of telescopic objective in system, and output end is coupled to IRFPA by coupling lens. By calibrating the position of each fiber in IRFPA, together with the mapping relationship between input and output of fiber bundle, a look up table is established. With the table, we can reconstruct the line object image. According to the scanning period of system, we can get the infrared scanning image.

This paper describes a high performance of opto-mechanically scanned millimeter-wave imager for airport security. It employs a crank-rocker mechanism to generate a high speed line scanning, which produces a horizontal FOV (field of view) of 30°. Accompanied by a frame scanning mirror of ±18° in the vertical direction, it brings about a two-dimensional scan of the scene of 146cm×75cm which is 1 meter away from the system. By this scanning mechanism, we use a single channel of a 94GHz receiver to collect the radiation from a convex lens which acts as the focusing element. Then the output of the receiver is passed to an A/D converter and is displayed on a conventional PC. The new scanning arrangement meets these requirements and has been being developed into a high performance, low-cost, and compact prototype system which hopefully will meet the present and future needs for millimeter-wave and terahertz imaging.

Signal processing is pivotal to laser radar system. Information like range, target's signature, etc. can be obtained from the processed laser signals. The received laser pulses for pulse laser radar are modeled. A wavelet filter is designed to denoise the contaminated laser signals. For the given laser signals, the filter based on the combination of correlation and thresholding is proposed. The gain of the filter is compared with the traditional thresholding method. It is shown that the combination of the correlation and thresholding denoising method is more effective for the weak laser radar signal processing compared with the traditional thresholding method.

A thermal infrared(MWIR or LWIR) integral imaging(II) system is proposed for acquiring and displaying 3D surface infrared emission radiance information of a real target. To intuitively analyze infrared integral image quality, we perform the numerical simulation and reconstruction of thermal integral image based on the modeling of sensor physical effects. Specifically, the 3D object with thermal infrared radiance texture is first focused into infrared elemental images by combining the virtual model of infrared microlens array and the response characteristics of detector array. Further, the displayed thermal elemental images are obtained by simulating main degradation factors including the spatial filtering blur, sampling effects, and spatial-temporal noise involved in practical infrared sensor. Finally, the thermal infrared 3D integral image is reconstructed by plane-plane reconstruction technique (PPRT) method based on the degraded elemental images. Their simulation results are demonstrated and analyzed. To the best of our knowledge, this is the first time to study thermal infrared II system and implement computational II reconstruction by considering thermal sensor physical effects.

The development of the un-cooled infrared imaging technology from military necessity. At present, It is widely applied in industrial, medicine, scientific and technological research and so on. The infrared radiation temperature distribution of the measured object's surface can be observed visually. The collection of infrared images from our laboratory has following characteristics: Strong spatial correlation, Low contrast , Poor visual effect; Without color or shadows because of gray image , and has low resolution; Low definition compare to the visible light image; Many kinds of noise are brought by the random disturbances of the external environment. Digital image processing are widely applied in many areas, it can now be studied up close and in detail in many research field. It has become one kind of important means of the human visual continuation. Traditional methods for image enhancement cannot capture the geometric information of images and tend to amplify noise. In order to remove noise and improve visual effect. Meanwhile, To overcome the above enhancement issues. The mathematical model of FPA unit was constructed based on matrix transformation theory. According to characteristics of FPA, Image enhancement algorithm which combined with mathematical morphology and edge detection are established. First of all, Image profile is obtained by using the edge detection combine with mathematical morphological operators. And then, through filling the template profile by original image to get the ideal background image, The image noise can be removed on the base of the above method. The experiments show that utilizing the proposed algorithm can enhance image detail and the signal to noise ratio.

To simultaneously modulate and transmit 10-Gb/s baseband and 20-GHz microwave signals on a single wavelength using single-sideband (SSB) modulation technique, a novel ROF scheme is proposed and verified by simulation. Based on a Dual-Parallel Mach-Zehnder Modulator (DPMZM) the scheme can carry the microwave signal on the upper sideband(USB) and the baseband signal on the lower sideband(LSB). It is to be seen from the simulated results that the crosstalk between the signals with dual services is very small. By means of subcarrier-multiplexing (SCM) technique, the optical 20-GHz microwave wave carrier is generated to carry 155-Mb/s baseband signal and 10-Gb/s baseband signal is imposed on the original optical carrier via SSB modulation. The simulated results of BER and the eye diagram are achieved separately. The signals with dual services are successfully transmitted over 50-km single-mode fiber.

In the progress of wavenumber traceability using polystyrene films, different peak-seeking algorithms are discussed in this paper. Conclusion shows that in commonly used methods, spline method, center of gravity method and the second derivative method, spline method is better than the others with simple algorithm and good agreement. It is strongly recommended to use in practical for calibrating FTIR spectrometer.

Low-resolution of terahertz (THz) imaging troubled its applications in the field of medical diagnosis and security inspection. The continuous wave (CW) THz imaging system utilizing a pyroelectric detector has been realized. The two crucial factors were analyzed in theory and verified in experiment; a high-quality THz image with the resolution of 0.4mm was obtained by choosing suitable imaging parameters. In our experiment the THz wave frequency of 2.53 THz, the spot size of 1.8 mm and the step length of 250 μm were selected to achieve high quality THz image. We also image several samples with different materials utilizing this system, and the results were very good.

The radiant cooler is used to cool optics and detectors to reduce signal noise in infrared (IR) telescopes. In-orbit radiant cooler could be contaminated by excessive molecular, particulate and outgassing. The contamination can change the emittance, solar absorptance and scattering of the surface of optical reflector and earth shield. The paper calculates the effection of contamination on the thermal properties of radiant cooler. The working performance degrades a lot when the optical screens are contaminated. Anti-contamination is emphasized for the radiant cooler through design, manufacture, tests and flight procedure for quantitative applications of remote sensing data. Low outgassing materials, reasonable outgassing channels and outgassing heaters are applied to the radiant cooler to reduce the potential contaminants. The flight performance of the cooler meets with the design requirements.

A terahertz time-domain spectrometer is employed to study various properties of jade, including the kind identification and polarization analysis. The characteristic absorption spectra and refractive index of jade are obtained in the range of 0.2 to 2.6 THz. Studying the absorption spectra and the transmission temporal THz waveform with two peaks, which were confirmed to be coming from ordinary and extraordinary beams, respectively, and result in fake absorption features. A practical ways are suggested to remove the fake absorption features and therefore the real absorption spectra of jade which accurately indicate the information of the samples can be obtained.

Degenerate pump-probe experiments have been performed with HgCdTe and GaInNAs thin films. The differential transmission versus probe delay time shows a negative value for both films, indicating photoinduced absorption from the trap states. After the negative minimum the differential transmission resumes to zero with long time constants. A rate equation formalism has been employed to model the carrier dynamics. The calculations fit the experimental differential transmission very well. The extracted time constants show that the carriers in the trap states of GaInNAs decay to the equilibrium state with a single time constant of 1.2 ns, while those in HgCdTe shows two time constants of 0.9 ns and 13 ps, respectively. This implies that there exist two types of deep level traps, fast and slow, in HgCdTe thin films.

Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. In this paper the spectral characteristics of air pollution gas, sulfur dioxide and hydrogen sulfide, had been measured with THz-TDS in the range of 0.2-2.6THz. The result shows that both the gases have equi-spaced absorption peaks and different gases have different intervals. We also investigated the influence of pressure on absorption spectrum by changing the pressure of the gases in a chamber. The experimental results indicate that the absorption peaks become sharper with increasing the pressure. Our experiments prove that terahertz Time-Domain Spectroscopy technique should be a powerful candidate for detecting atmospheric pollutants.

Terahertz ray, as a new style optic source, usually means the electromagnetic whose frequencies lies in between 0.1THz~10THz, the waveband region of the electromagnetic spectrum lies in the gap between microwaves and infrared ray. With the development of laser techniques, quantum trap techniques and compound semiconductor techniques, many new terahertz techniques have been pioneered, motivated in part by the vast range of possible applications for terahertz imaging, sensing, and spectroscopy. THz imaging technique was introduced, and THz imaging can give us not only the density picture but also the phase information within frequency domain. Consequently, images of suspicious objects such as concealed metallic or metal weapons are much sharper and more readily identified when imaged with THz imaging scanners. On the base of these, the application of THz imaging in nondestructive examination, more concretely in large scale circuit failure inspection was illuminated, and the important techniques of this application were introduced, also future prospects were discussed. With the development of correlative technology of THz, we can draw a conclusion that THz imaging technology will have nice application foreground.

A design of light modulator for THz amplitude and phase modulations has been presented in this paper. Simplest versus of the Drude model is adopted, in which the collision damping is independent of the carrier energy. In our experiment, we use THz-TDS as THz source and detector. A laser whose wavelength is 808nm was used to irradiate the intrinsic Si(high-resistance), so as to let it generate the Photo-carriers ,and to influence the conductance . The Photo-carriers will change the absorption coefficient of the THz wave and also influence the dielectric of the sample, hence to control the characteristics of the THz wave in the silicon . By changing the light intensity , due to the different photon-generated carrier concentration ,the single transmission of the THz wave in the silicon wafer sample is changing remarkable . Theoretically, the modulation depth can be more than 80%. we present our design of light modulator for THz, and show the Digital simulation of our design. Also, according to this design theory, Optical/electronic integrated modulation of THz can be realized, that will be our future work.

Excitonic optical absorption in quantum wells (QWs) under intense terahertz (THz) waves polarized along the grown-direction is investigated. The characteristics induced by the strong THz field in the optical absorption spectrum in the QWs near the band gap edge is analyzed by coherent wave approach. The calculated results with and without the presence of THz field are presented. It shows that the excitonic absorption peaks may split or broaden when an intense THz field is applied. The presence of an intense THz field results in the formation of replicas in the absorption spectrum. The replicas are not symmetric and presence on both sides of the main excitonic peaks due to the Coulomb interaction between electrons and holes.

In this paper, the electro-optic effect of the crystals was observed and discussed in the terahertz range, and theoretic analysis was implemented on the experiment's feasibility. Three crystals, ZnTe, GaAs and Si were chosen as the experimental group in the research, and the way to use terahertz TDS system properly to measure the spectrum changes of refractive indexes of crystals under voltage 0-200 V with 10 cm distance in terahertz range is demonstrated. According to the measurements, the refractive index of GaAs had obvious changes around 0.0932 in the frequency from 800 GHz to 2 THz, the refractive index of ZnTe has comparatively small changes around 0.015, and the refractive index of Si hardly changes. The results have validated that the refractive indexes of electro-optic crystals ZnTe and GaAs have changed as the intensity of the external electric fields varied appropriately. And that may have potential applications in photoelectric devices in the terahertz range. Both theoretic analysis and experimental results demonstrate the experimental study is reasonable and successful.

A technique of fiber array structure of visible to infrared image transducer for infrared imaging control and guide was discussed. Be different from the normal fiber array, the structure here is micro-fabricated on quartz glass covered with visible absorb member in front of the fiber. The fiber array structure works in vacuum and cooling chamber. The 3D model of fiber array structure for finite element analysis based on the secondary radiation was established. The material parameter, including density, specific heat and thermal conductivity, and the structure size including section size, length of fiber array transducer for temperature and time character were studied. The simulation results show that the thermal conductivity and length of fiber array are key parameters for transducer's property, and the optimized parameters for fiber array structure transducer were given. The fiber array structure of visible to infrared image transducer has the advantage of higher spatial and temperature resolution, and less manufacture cost. The optimized parameter for fiber array visible to infrared image transducer can reach the frequency of 100Hz and higher temperature of 250°C in case of increasing impulse power which can be used as infrared scene projector in hardware-in-the-loop simulation experiment.

The ALMA Band 9 receiver cartridge (600-720 GHz) based on Dual Sideband (DSB) superconductor-insulatorsuperconductor (SIS) mixer is currently in full production. In the case of spectral line observations, the integration time to reach a certain signal-to-noise level can be reduced by about a factor of two by rejecting an unused sideband. The goal is to upgrade the current ALMA band 9 cartridge to a full dual-polarization sideband separating (2SB) capability, with minimal-cost upgrade path. A new compact and modular sideband separating mixer was designed, and a prototype manufactured. The individual SIS mixer devices in the 2SB block are implemented as conventional Band 9 DSB mixers, so that existing devices can be reused and tested individually. Any ALMA DSB developments contribute to the 2SB upgrade. The first experimental results demonstrate noise temperature from 300K to 500K over 80% of the band, which will be improved to fit the ALMA requirements. Nevertheless, the frequency response for 2SB is the same as for DSB, showing that the RF design is still valid, even with different SIS mixer devices. The quality of the RF and IF design is confirmed by a sideband rejection ratio of about 15 dB, which is within the ALMA spec (>10dB ).

Huygens-Fresnel principle and half-wave method are usually used to explain the diffraction effect as the light passing through a hole. We present a new simple method to enhance the terahertz signal intensity by using a small hole. We found that in the terahertz time-domain spectroscopy, the terahertz signal enhances by 13.87% as a hole with certain size is put in a certain position of the terahertz beam path. This effect can be fully explained by using Huygens Fresnel principle. Therefore, in the condition of terahertz emitter and detector are unchanged, by using this method to enhance the terahertz signals is of great significance.

In this paper, we propose an efficient air-core Terahertz (THz) fiber with high birefringence and low modal absorption loss. The photonic crystal fiber has a triangular-lattice with circular subwavelength air-holes in the microstructured cladding and elliptical subwavelength air-holes in the core. In this structure, the effective index of the core is above that of the cladding, which leads to a better confinement of the field and ensures the low loss characteristic for THz guiding. With elliptical air-holes in the core, the proposed THz fiber exhibits high birefringence. The background medium is the polymer material with low absorption in THz region. The proposed design has been simulated based on the finite element method with anisotropic perfectly matched layers (PML) absorbing boundary condition. Numerical simulations show that with a moderate ellipticity of the elliptical air-holes in the core region, the proposed THz fiber can exhibit high birefringence on a level of 10^-2 in a 0.2THz to 2.0THz frequency range. And the THz fiber's guiding loss caused by material absorption can be reduced effectively by the addition of more air holes in the core region.

The authors have developed the mobile robot which can be programmed by command and instruction cards. All you have to do is to arrange cards on a table and to shot the programming stage by a camera. Our card programming system recognizes instruction cards and translates icon commands into the motor driver program. This card programming environment also provides low-level structure programming.

Scannerless imaging laser radar has been a focus of research in these years for its fast imaging speed and high resolution. We introduced a three-dimensional imaging laser radar using intensified CCD as the receiver with constant gain and line modulated gain. The distance map of a scene is obtained from two intensity images. According to the transmission characteristics of the imaging system, a model of degeneration of the gray images is established and the range accuracy of imaging laser radar based on this model is analyzed. The results show that the range accuracy is related with the reflectivity, the actual distance and some other factors on the fast-distance-varying region, while it is mainly concerned with shot noise for the flat area. On the basis of the cause of measurement error and the distribution characteristics of noise, a method which uses iterative restoration algorithms on obtained intensity images is presented, Simulation is carried out and the results show that root mean square error of distance map obtained with this method is decreased by 50%, compared with the distance map obtained by measurement. Finally the restoration results of radar images are demonstrated to verify the effectiveness of this method.

THz imaging technology will be potentially used in structure's defects detection, package inspection, on line product quality control, security screening or other nondestructive testing fields. But due to its long wavelength, it is difficult to obtain high spatial resolution and large focal depth simultaneously for conventional imaging systems. In this paper, diffraction free quasi-Bessel beams are used in THz imaging system to enhance the focal depth with high spatial resolution. PE conical lenses were designed and fabricated to generate quasi Bessel beams. Numeric simulations demonstrated that with suitable parameters of the conical lens, the diffraction free propagation distance and effective focal depth of the imaging system are easily reached up to 165mm, 100mm, respectively. A THz imaging system based on quasi-Bessel beams was established, and results were in good agreement with simulations. Furthermore, the inner defects built-in artificially in phenolic foam samples with diameter of 0.4mm were figured out successfully.

The carrier dynamics and terahertz photoconductivity in the n-type silicon (n-Si) as well as in the p-type Silicon (p- Si) have been investigated by using femtosecond pump-terahertz probe technique. The measurements show that the relative change of terahertz transmission of p-Si at low pump power is slightly lower than that of n-Si, due to the lower carrier density induced by the recombination of original holes in the p-type material and the photogenerated electrons. At high pump power, the bigger change of terahertz transmission of p-Si originates from the greater mobility of the carriers compared to n-Si. The transient photoconductivities are calculated and fit well with the Drude-Smith model, showing that the mobility of the photogenerated carriers decreases with the increasing pump power. The obtained results indicate that femtosecond pump-terahertz probe technique is a promising method to investigate the carrier dynamics of semiconductors.

Based on the spherical vector wave functions, we research the scattering of a homogeneous chiral sphere to a plane wave. The expansion coefficients of scattered fields and internal fields are obtained through the boundary condition at the sphere interface. The logarithmic derivatives of Ricatti-Bessel functions are introduced in order to avoid the numerical overflow of high-order terms or larger argument spherical Bessel function and the problem of the accumulative error in the matrix calculation. Thus, the scattering characteristics of a chiral sphere with larger size parameter can be studied numerically. Moreover, the influence of chiral parameter on the polarization properties is also numerically analyzed.

Since noise can undermine the effectiveness of information extracted from hyperspectral imagery, noise reduction is a prerequisite for many classification-based applications of hyperspectral imagery. In this paper, an effective three dimensional total variation denoising algorithm for hyperspectral imagery is introduced. First, a three dimensional objective function of total variation denoising model is derived from the classical two dimensional TV algorithms. For the consideration of the fact that the noise of hyperspectral imagery shows different characteristics in spatial and spectral domain, the objective function is further improved by utilizing two terms (spatial term and spectral term) and separate regularization parameters respectively which can adjust the trade-off between the two terms. Then, the improved objective function is discretized by approximating gradients with local differences, optimized by a quadratic convex function and finally solved by a majorization-minimization based iteration algorithm. The performance of the new algorithm is experimented on a set of Hyperion imageries acquired in a desert-dominated area in 2007. Experimental results show that, properly choosing the values of parameters, the new approach removes the indention and restores the spectral absorption peaks more effectively while having a similar improvement of signal-to-noise-ratio as minimum noise fraction (MNF) method.

Direct detection mm/sub-mm wave warm-carrier bipolar narrow-gap Hg_1-xCd_xTe semiconductor bolometers that can be used as picture elements in THz sensitive arrays, are considered. The response of Hg_1-xCd_xTe warm-electron bolometers was measured in v=0.037-1.54 THz frequency range at T=68-300 K. Bipolar semiconductor warm-electron bolometer theoretical model was developed. In the detector considered the electromagnetic wave propagates in semiconductor waveguide, heats electrons and holes, creates their excess concentrations, as well as, the electromotive forces. These effects cause the bolometer response voltage. Experimental results confirm the model main conclusions. Because of response time defined by carrier recombination time in HgCdTe layers (τ~10-8-10-6 s) and the noise equivalent power that can reach NEP_{300 K~}4×10-10 W/Hz1/2 in mm-wave region, the arrays on the base of HgCdTe bolometers can make them promising for active relatively fast frame rate sensitive applications. At liquid nitrogen temperature NEP can lowering up to NEP_{77 K~}10-11 W/Hz^1/2. Embeded p-n-junctions in HgCdTe can increase the detectors responsivity by an order.

Passive millimeter-wave imaging is attractive due to the ability to obtain images in low-visibility conditions. In this paper, a passive millimeter-wave imaging method using photonic processing is presented. The principle of the millimeter-wave photonic signal processing method is described. The relationship between the signal conversion gain and the component parameters is discussed. The noise characteristic of this detection method is analyzed. A millimeterwave radiometer using photonic processing is presented in this paper. A passive millimeter-wave scanning imaging system using this processing method was implemented. The imaging experiment results show that this imaging method is effective.

For science and technology, the level of science and technology is determined by the measurement accuracy and efficiency to some extent. Contact resistance can not be ignored in precise measurement. Because the measured object is not directly contacted with infrared measurement device, there is no friction. Infrared measurement has the advantage of high sensitivity, fast response and so on. In this paper, the reasons for the temperature rising of the contact resistance and its harm and the importance of measuring the temperature of the contact resistance in precise measurement are analyzed firstly; then some theories of the infrared detection technology are introduced; finally, an infrared temperature measurement system based on SCM is designed.

The carotenoid molecules associated with the proteins perform the important physiological functions of harvesting, transferring and dissipating light energy in the light-harvesting process. Especially, these functions originate from changes in the electronic and molecular configurations of the carotenoid molecules under the influence of intermolecular or intramolecular interactions with the apo-protein. Terahertz spectroscopy is a power tool for the prediction of the configuration or conformation of the carotenoid and non-covalent interactions. All-trans beta-carotene molecule has eleven conjugated double bonds in the polyene chain with all-trans configuration. In this paper, the low-frequency vibrations of all-trans beta carotene molecule were firstly observed. One hand, the vibrational modes of 0-3 THz were obtained by terahertz time-domain spectroscopy (THz-TDS) and Fourier transform far-infrared (FT-FIR) spectrometer, respectively. The absorption spectrum of all-trans beta-carotene molecules were also presented in this frequency region. On the other hand, the other vibrational modes in the range of 3-20 THz were only obtained through FT-FIR spectrometer. There exhibit a lot of rich and distinct vibrational peaks. The terahertz spectra of all-trans beta-carotene molecules represent unique fingerprints of the molecular geometries structures of both beta-ionone and long conjugated double bonds. And the environment of the molecule leads us to the conclusion that THz technique can be used for the recognition of the organic molecules and their conformations.

Continues wave terahertz imaging has been used widely in the field of security inspection and nondestructive examination because of its simplicity and stability. In this presentation, we proposed an image method with continues wave terahertz interferometry to obtain the sample's phase information. In the experiment, a reference terahertz beam was added into the exiting continues wave terahertz imaging system to be a Michelson interferometer. With three maps obtained at three fixed phase-shift positions, a phase image is obtained by using a phase shift algorithm. Afterwards, this phase image is unwrapped to get its accurate phase profile. By this method, a bulk of foam with two height steps structure is imaged. The result shows that the inner structures of samples can be identified clearly and the relative optical depth profiles of samples can be obtained.

The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent measurements are also performed to verify this model.

The modes in a metallic waveguide loaded with a high permittivity dielectric rod may possess similar dispersion relations to the modes in the left-handed metamaterial (LHM) waveguide. Therefore, such dielectric-loaded metallic waveguide may also support slow light propagation. The slow light in such waveguide is numerically studied. The properties and the existence conditions of slow light modes in such waveguide are also numerically studied. The results show that the wavelength of slow light varies with the parameters of the waveguide and that high-contrast between the dielectric rod and the air is necessary of existence of slow light modes. The linearly tapered waveguide are proposed accordingly to realize the "trapped rainbow" phenomena. The practical tapered lossy waveguide is also investigated. It is shown that the slow light with low loss can be achieved in a realistic waveguide. Moreover, a novel notch filter based on such slow light waveguide is proposed.

We have achieved a Terahertz (THz) DFG system based on a walk-off compensated intracavity pumped dualwavelength KTP OPO employing two identical KTP crystals. The KTP OPO is doubly resonant and works near the degenerate point at 2.128μm, which doubles the quantum efficiency compared with DFG using pump pulses around 1μm. This THz source is simple and compact, about 10×10×40cm2 in size. Besides lower threshold and better stability, the walk-off compensated KTP OPO greatly improves the pump beam quality and enhances the DFG conversion efficiency. With an 8-mm-long GaSe crystal, the generated THz tuning range is from 0.186THz to 3.7THz with the maximum output voltage of 489V on the bolometer at 1.68THz. An average enhancement of 76.7% for the THz energies is realized using the walk-off compensated KTP OPO than a common one. The conversion efficiency can be improved with a longer and better GaSe crystal.

In this paper, we proposed a method for THz sub-comb generation based on optical rectification. The result of our calculation indicated that THz pulse train, generated by surface-emitted optical rectification (OR) of femtosecond (fs) laser pulse in a periodically poled lithium niobate (PPLN), has a comb-like spectrum. The theoretical analysis was based on radiating antenna model. The characteristic of this THz sub-comb was analyzed both in frequency and time domain. The mechanism of this phenomenon was explained both by spectral interference between early and late pulses and by high-order quasi phase matching. THz sub-comb generated by this method can cover a large bandwidth and have a wide free spectral range.

In this work, modal birefringence and loss characteristic for the fundamental mode in terahertz (THz) polymer elliptical-tube waveguides are investigated by using a full vector finite element method (FEM). Numerical results show that this kind of waveguide has high birefringence (~10^-2) and better loss property as a large part of mode power is trapped in the air-core inside the polymer elliptical-tube. Dependence study of the birefringence on several parameters is also provided and numerical results show the birefringence increases as refractive index and thickness of polymer tube increased.

With the development of terahertz (THz) technology, an efficient propagation waveguide is essential for the construction of compact THz devices. Hollow core photonic crystal fiber with a large air core at the center and a cladding formed by a periodic arrangement of polymer tubes has been demonstrated in this paper. The guidance mechanism is based on anti-resonant reflection from struts of solid material in the cladding. Since most electromagnetic field is dominated in the air core, hollow core fibers have obvious advantages in lower absorption. The propagation characteristics of the fiber, such as the mode field distribution and the loss coefficient are numerically investigated through the finite element method. The result shows that an effective way to reduce the absorption is to enlarge the central air core and reduce the overlap between the field and material.

High-power nanosecond pulsed THz-wave radiation was achieved via a surface-emitted THz-wave parametric oscillator (TPO). The effective parametric gain length under the condition of noncollinear phase matching was calculated to optimize the parameters of the TPO. Only one MgO:LiNbO₃ crystal with large volume was used as gain medium. THz-wave radiation from 0.8 to 2.9 THz was obtained. The maximum THz-wave output was 289.9 nJ/pulse at 1.94 THz when pump power density was 211 MW/cm², corresponding to the energy conversion efficiency of 3.43×10^-6 and the photon conversion efficiency of about 0.05%. The far-field divergence angle of THz-wave radiation was 0.0204 rad at vertical direction and 0.0068 rad at horizontal direction.

Electronic devices are widely used in various industries, their temperature distribution cannot be obtained by traditional test methods. In recent years, simulation softwares are used to simulate the thermal characteristics of electronic devices and play a positive role on the reliability improvement, on the contrast, their validity cannot be verified. In this paper, the chip temperature rise process is simulated by ICEPEAK software. Some factors that change thermal characteristics are analyzed. The actual working temperature obtained by the thermal microscope is compared with the simulation temperature. The validity of simulation temperature is tested and the relation is built between the actual temperature and simulation temperature. Finally, it is pointed that thermal microscopes are the development direction on the electronic devices design and reliability testing.

Simultaneous generation and transmission of 10-Gb/s baseband signal and 20-GHz microwave signal with 155-Mb/s on-off-keying (OOK) data on a single wavelength over 50-km-long fiber link based on a dual-parallel Mach-Zehnder modulator (DPMZM) are investigated. After simultaneous modulation of the baseband signal and microwave signal at central office (CO), the hybrid signals are separated by interleaver(IL) or fiber Bragg grating (FBG) at base station (BS). The center wavelength spacing and bandwidth of IL, also the reflection ratio, center wavelength and bandwidth of FBG are to be considered carefully as the baseband and microwave signal are only tens of GHz spacing and hard to be separated with each other. Through theoretical analyses and simulation, for the demonstrated hybrid transmission system, the relations of Q factor with the reflection ratio and bandwidth of FBG are analyzed separately in different fiber links (SMF and DSF).

A theoretical model is proposed to study quantitative differences in the size of large-aperture between circle polarization shift keying (CPolSK) and on-off keying (OOK). The quantitative differences can be analyzed with the impact from atmospheric condition, link length, and communication wavelength. Numerical results show that FSO CPolSK systems with longer communication wavelength can reduce the size even smaller than the systems using OOK, while it can be not obvious with increasing link length. Meanwhile, increasing average signal-to-noise ratio (SNR) leads to a reduction of the difference in aperture size. These results can be helpful for FSO systems design.

In this paper, we present the modeling and measurement results of niobium titanium nitride hot electron bolometer mixers with different sizes at terahertz frequencies. A distributed hot spot model which is based on solving a heat balance equation is employed to characterize current-voltage curve, electron and phonon temperature distribution along superconducting microbridge, intermediate frequency gain bandwidth and intrinsic noise temperature of the mixers. The simulated intermediate frequency gain bandwidth decreases with the increase of microbridge length, which is in good agreement with measured results. A difference of factor of several tens exists between the calculated and measured mixer noise temperature, which is probably due to the disfigurement of waveguide structure and unknown noise from the mixer.

We study theoretically that a resonant response with a high quality factor could be achieved in a planar positive or negative metamaterials by weakly breaking the geometrical symmetry of its unit cells. The trapped mode resulting from broken structures is investigated using the finite element method and the dependence of the quality factor on structural parameters is also discussed.

We have proposed and investigated a radio-over-fiber (ROF) system transmitting 100Gb/s orthogonal frequency division multiplexing (OFDM) signals by simulation. The ROF system can transmit vector modulation formats, such as OFDM signal. The simulation results show that carrier suppression technique can be used to achieve two 50Gb/s OFDM signals over 20km SMF successfully.

With the combination of neuro-genetic approach and laser-induced breakdown spectroscopy (LIBS), an improved method is proposed to predict the concentrations of Ni, Zr and Ba in soil samples. In this method, an artificial neural network (ANN) based on gradient descent with momentum and adaptive learning rate back propagation (GDMABP) algorithm is used. Simultaneously, an optimization strategy based on genetic algorithm (GA) is employed for selecting number of neurons in hidden layer and momentum coefficient in GDMABP ANN and to obtain an optimized network. Subsequently, the network is used to predict concentration of Ni, Zr and Ba from the tested LIBS data. The approach of neuro-genetic for LIBS analysis is described in detail. The predicted results are compared with those obtained from conventional calibration curve method. Overall, the method of combining neuro-genetic approach with LIBS is capable of predicting elemental concentration.

Conventional ultrasonic thermography (thermosonic or sonic infrared imaging) is a technique in which acoustic energy is coupled to the structure by means of an acoustic transducer in contact with the sample, the captured temperature at the defect areas by an infrared camera is relatively higher than that of the surrounding area. The primary problem of this technique is that the acoustic horn must be mechanically in contact against the tested sample with an applied force. Therefore, the potential for damaging the structure especially for the filmy, brittle and fragile structure can't be ignored. In this paper, a new NDE technique based on a non-contact ultrasonic excitation thermography has been presented. The technique utilizes a redesigned ultrasonic horn to excite the sample in a non-contact fashion, and an infrared camera to monitor the variation of the surface temperature. The presented experimental results show that the non-contact ultrasonic excitation thermography has some potential in NDE application.

The rut results based on the line-laser rut measurement are often subjected to the vehicle bumps, vehicle pitch changes in practical applications. The principle of line-laser rut measurement is described and the factors are analyzed from the perspective of optical imaging. A new method of symmetrical line-laser rut measurement is proposed. This method uses symmetric line-laser imaging system and can effectively reduce the rut test errors caused by the vehicle bumps, vehicle pitch changes. Experimental results show that the symmetric line-laser rut measurement can be used to detect road surface rut.

The asymmetry imaging spot caused by the CCD saturation and the scattering of uneven road surface usually leads to lower accuracy in the road surface detection. A new method of the symmetric displacement sensor for the road measurement is given. The sensor consists of two symmetrical image systems and two line scan CCDs which are arranged reversely. The centroidal algorithm is adept to calculate the coordinates of the image point of each CCD. The finial displacement is given by the average of the coordinates of the image point of two CCDs. The experimental results indicate that the symmetrical laser displacement sensor can reduce the asymmetry imaging test error and improve the precision of measurement effectively. It is very suitable for the pavement evenness, rut and texture detection.

This paper reports a preliminary work on a feasibility study of applying terahertz (THz) technology for pecan quality evaluation. A set of native pecan nuts collected in 2009 were used during the experiment. Each pecan nutmeat was manually sliced at a thickness of about 1mm, 2mm, and 3mm and a size of about 2cm (length) ×1cm (width). Pecan shell and inner separator were also cut into the same size. The absorption spectra for the nutmeat slices, shell, and inner separator were collected using a THz time-domain spectroscopy (THz-TDS) developed by a group of researchers at Oklahoma State University. The test results show that nutmeat, shell, and inner separator had different absorption characteristics within the bandwidth of 0.2-2.0 THz. To study the capability of insect damage detection of the THz spectroscopy, the absorption spectra of insects (living manduca sexta and dry pecan weevil) were also collected. Due to high water contents in the insects, very obvious spectral characteristics were found. The results from the preliminary study show a potential of THz technology applied for quality detection of bio-products. However, since bio-products mostly have high water content and are handled under an environment with certain levels of water content, practical issues needs to be further investigated to make the THz technology a feasible tool for quality evaluation.

For the limitation of detecting materials, the images from the novel un-cooled infrared system based on visible light readout are blurry and have low contrast. The images also have more noise and larger holes. Especially after pseudo-color processing, the noise and holes will become much clearer. For the characteristics of images in the un-cooled IR system, the traditional image processing methods for IR images are not suitable for the image in our research. Therefore, an advanced one-dimensional triple wavelet analysis in row for infrared images is presented based on the characteristics of un-cooled infrared system. In this method, the triple wavelet decomposition is made in each row of image, and detail coefficients and approximation coefficients of each row can be obtained. The detail coefficients in the first time of wavelet decomposition express the whole details of image containing noise and the edge of object. So after low-pass filter, the noise in the image can be suppressed. By the wave reconstruction made between the approximation coefficients in triple wavelet decomposition and the detail coefficients after low-pass filter, each row in images without noise and holes can be gained. In wavelet reconstruction, a weight being proportional with the filtering window is multiplied with detail coefficients. The weight can make sure the gray value of whole picture and the contrast cannot be lower after low-pass filter. The images from un-cooled infrared system are processed in the computer with the software of MATLAB. The results support that compared with traditional methods the novel method can be more effective to eliminate the noise and fill holes, and better response to the temperature details of objects.