This PDF file contains the front matter associated with SPIE Proceedings Volume 10844 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

High-quality Yb-doped Y3Al5O12 [yttrium–aluminum garnet YAG] crystals and Na, Ba co-doped Yb:YAG crystals with diameter of 65mm were grown from melt by the Czochralski method. The chemical of the two crystals are (Yb_0.1Y_0.899)₃Al₅O₁₀ and (Na_0.0005Ba_0.0005Yb_0.1Y_0.899)₃Al₅O₁₀. The structure, photoluminescence properties and scintillation yield were studied. The prepared samples are identified as pure garnet structure by the XRD results, indicating that the co-doping of a small amount of Na, Ba ions has no influence on the structure of the host. Thermoluminescence glow curves with the temperature showed that there were 100℃ and 260℃ thermoluminescence peaks in the two kinds of crystals, but the peak intensity of co-doping sample decreased, which suggested the number of defects decreased significantly. Light output in co-doped crystals reaches 110% comparative to Yb:YAG crystals and the sensitivity increased by 40%. This suggests that trace ions co-doping may be a possible way to reduce the crystal defect and increase the optical output.

Conventional wavelength modulation spectroscopy is improved by logarithmic-transformed data processing and differential detection for trace gas sensing. The optic intensity modulation is isolated from the gas absorption induced laser power attenuation via the logarithmic-transformation, and then it is balanced out by differential detection. The theory is validated by the detection of P(6) ammonia absorption line belonging to the v₃ + v₄ combination band in a stainless tube with effective path length of 24.5 cm, under room temperature (296 K) and atmospheric pressure (1.01e5 Pa). The second harmonic is recovered while the residual amplitude modulation and distortion of harmonic are eliminated. A 0.7 ppm (part per million) detection limit is estimated on the assumption that the signal is equal with the noise. Excellent repeatability is observed from continuous measurements of 20 times during 240 hours. Standard deviation of the measured ammonia mole fraction and the simulation data is 1.1%. All of these inspire results indicate that our strategy is an ideal option for trace gas detection.

Photodarkening(PD) in Yb-doped fiber is one of the power limiting factor for long-time operation in high power fiber lasers and amplifiers. In order to achieve Yb-doped fiber laser and amplifier with high output power, a steady-state rate equations considering the amplified spontaneous emission (ASE) and PD losses has been established. Thermal effects and output power characteristics of high power fiber laser and amplifier are investigated. Transverse and longitudinal temperature distributions in fibers have been calculated by solving thermal conduction equations. We theoretically analyzed the PD losses and temperature in Yb-doped fiber laser and amplifier, the simulation results show that with the PD losses increasing, then the laser power drop quickly and we find that higher doped concentration and larger PD losses will lead higher temperature, so we should choose suitable doped concentration fiber and decrease PD losses to achieve higher output power.

We present an analytical theory based on a steady-state rate equations that describe pump power, stimulated Brillouin scattering (SBS) power, amplified spontaneous emission (ASE) and output power of a single-frequency 1018nm short wavelength fiber amplifier. A detailed model that accounts for amplified spontaneous emission (ASE) and stimulated Brillouin scattering (SBS) in relation to the ASE gain, Brillouin gain, fiber length, seed power, the linewidth of seed laser, and available pump power in both co-pumped, counter-pumped and bidirectional configurations is developed. It is found that when fiber length is optimized, the amplifier output power will increase with available pump power. In order to mitigate the SBS process, we can shorten the fiber length or reduce the seed laser power. Although higher output power is obtained with higher seed power, the SBS power will increase, and we find that the same amplifier efficiency is obtained with different pumped configuration, counter-pumped configuration mitigate SBS is more effective than co-pumped configuration and bidirectional configuration. We also calculate the output power and SBS power which consider the linewidth of seed laser by different pumped configuration, we also find that broader linewidth of seed laser can achieve lower SBS output power, but the change of laser power is unobvious with increasing the linewidth of seed laser. In order to suppress the ASE waves, we can shorten the fiber length or increase the seed laser power.

1018nm Short wavelength Yb3+-doped fiber laser can be widely used for tandem-pumped fiber laser system in 1 μm regime because of its high brightness, high beam quality and low quantum defect (QD). In order to achieve 1018nm short wavelength Yb3+-doped fiber laser or amplifier with high output power and high beam quality, a steady-state rate equations model considering the mode competition, bend loss has been established. We theoretically analyzed the mode competition in 1018nm short wavelength Yb3+-doped fiber laser and amplifier and the simulation results show that the when the bend radius is 5cm, the LP01 mode output power is higher than the other mode power in the fiber laser and amplifier. When the bend radius is larger than 5cm, the beam quality will decrease in fiber laser and amplifier especially for fiber laser, besides we calculated the mode power in the fiber amplifier at different power of seed laser, when the LP01 mode power is higher than the other, the beam quality will increase. At last we analyzed the evolution of transverse gain of every mode along the radial coordinate in fiber laser and amplifier. Our results can provide instructive suggestions when designing bend radius and the power of seed laser based fiber laser and amplifiers and can help to enhance the beam quality.

In this work, we establish a unified temporal-spatial model to study the temporal-spectral dynamics of Ytterbium-doped fiber lasers (YDFLs). Different from the previously reported theories, this model is capable of obtaining the temporal property of YDFLs from the relaxation oscillation region to the relative stable region in the time window of millisecond scale with the time resolution of sub-nanosecond scale. The simulation results reveal that the three temporal instabilities, i.e. sustained self-pulsing (SSP), self-mode locking (SML) and turbulence-like pulsing (TLP), coexist in a multilongitudinal mode YDFL. When the output power evolution of the YDFL is observed in different time scales, different temporal instability phenomena dominate in the observation. Along with the increase of pump power, a single regular SML pulse would gradually break up into irregular TLP pulses and the life of the SSP pulse envelop would decrease. Besides, the spectral evolution property of the YDFLs at different pump powers are given and significant spectral broadening is observed.

For study the mechanism of formation of self-generated magnetic field and proton generation in laser plasma interaction. This article based on the Maxwell’s equation applies the theoretical analysis and numerical simulation, the studied physical processes of self-generated magnetic field and proton acceleration in the interaction between ultra short laser pulse and plasma concave target, discussed provided the time evolution relationship of the distribution of self generated magnetic field induced by the non-parallel property of the temperature gradient and density gradient and proposed the laser-driven proton acceleration in plasma concave target irradiated by ultra short laser pulses with relativistic intensities. The results show that when laser injected the plasma concave target. The self-generated magnetic is generated on the surface of the plasma. Because of the nonparallel density gradient and the temperature gradient, this magnetic field considerably affects the processes of the absorption of laser energy, heat transmission and proton acceleration. Further research on this problem has significant potential applications in the realization of inertial confinement fusion, medical diagnosis, treatment and so on.

In this paper, a transient plasma is produced by focusing the 1064 nm radiation from a Q-switched Nd:YAG onto the one-yuan coin at room temperature in air at atmospheric pressure. Using the iterative Boltzmann algorithm, the plasma electron temperature of the one-yuan coin is calculated as 28144 K. Experiments show that the correlation coefficient increases from 0.197 to 0.997 as the number of iterations increases. Experimental results show that the laser induced one-yuan coin plasma meets the LTE model.

The propulsive properties of the energetic polymer glycidyl azide polymer (GAP) doped with carbon nanoparticles in the transmission mode were studied and a 1064nm Nd:YAG laser with a pulse width of 9ns was selected. According to the Propulsion performance parameter of GAP with different carbon nanoparticles contents and thickness, combined with plume image, the reasons for improving the propulsion performance of laser ablation GAP by carbon nanoparticles doping are analyzed and the design scheme of the structure composition of the polymer target is preliminarily explored. The experimental results show that the 1064nm laser absorption of the polymer GAP is greatly enhanced and the propulsion performance is obviously improved after doping with carbon nanoparticles, but the propulsion performance of the polymer can not be significantly improved by increasing the carbon contents higher than 1%. The GAP after doped with high carbon nanoparticles contents exhibits metal-like surface absorption characteristic and the absorption depth to laser decreases. Under the transmission mode, with the increase of target thickness, the incomplete ablation mass increases, which greatly reduces the utilization ratio of GAP. The optimal ablation efficiency of GAP target with thicknesses of 54μm was more than 250%, and plume images showed that ablation and decomposition were very sufficient. It is appropriate for the target of laser ablation micro thruster.

The effectiveness and efficiency of laser processing depends on absorption characteristics of materials. A combination of a low-energy supercontinuum with a high-energy narrowband laser was proposed to form a potential new laser source for materials processing. The broadband spectrum of the supercontinuum is expected to slightly change the properties of target materials by materials absorption, and then the narrowband laser is able to process the materials effectively. This new laser source was realized by seed pulse-shaping. The seed pulses were formed by a high and short pulse with a low and long pulse, which were generated from an electrically modulated laser diode operating at 1064nm. After being amplified, the pulses went through a section of photonic crystal fiber. The average output power and spectrum could be widely tuned as the pulse durations, amplitudes and relative delay time varied.

The investigation focuses on measuring the influence of crack and its width on wedge waves propagating along wedge tip by using laser ultrasound technique. Usually, ideal wedge is almost non-existent, the non-perfect wedge may bring in break and enormous economic losses. Therefore, it is necessary to investigate the characteristic of wedge waves propagating along line wedge with cracks. The wedge waveguide models with different cracks were built by using finite element method. For 20° wedge, multiple mode wedge waves were observed through B-scan. The width of crack of rectangle shape is 0.1mm, and the width are 0.01mm, 0.05mm, 0.1mm, and 0.2mm, respectively. Both reflected and transmitted waves are observed. Due to the dispersion characteristics, we observed the reflected and transmitted A₁, A₂ mode. Meanwhile, A₁ mode separated from the reflected and transmitted A₂ mode are also obtained as the wedge wave mode propagating to crack. As the width diverse, it is found that the propagating of wedge waves is almost no change. This study can provide theoretical guidance for the positioning and size estimation of wedge cracks.

We theoretically study the photoelectron momentum spectra of the negative hydrogen ions by few-cycle orthogonally polarized two-color (OTC) laser pulses. It is found that the photoelectron momentum spectra can be effectively manipulated in the polarized plane by few-cycle OTC laser pulses. The results qualitatively agree well with the prediction of the simple man’s model. Finally, the effects of the duration of laser pulse on the photoelectron momentum spectra are discussed. The present work is meaningful for the optical control of the laser induced photodetachment of negative ions.

In this letter, a single-longitudinal-mode (SLM) Tm:LuAG laser under room temperature condition using double Fabry-Perot etalons is reported . The maximum single-frequency output power is 93 mW with a slope efficiency of 4.1%. The single-longitudinal-mode laser can be used as a seed laser for coherent wind measurements and differential absorption LIDAR systems.

For the problem of low modulation rate and narrow modulation bandwidth of semiconductor lasers(LD),according to the LD rate equation, the expression of the relaxation oscillation frequency is derived.The influence of internal parameters on the modulation characteristics of laser is simulated from two aspects: time domain and frequency domain. The simulation results verify the correctness of the theoretical derivation. In addition, measures for improving the modulation characteristics of lasers are proposed. The results show that the larger modulation bandwidth and higher modulation rate can be achieved by increasing the steady state photon density and differential gain coefficient and reducing the photon lifetime and the gain saturation factor.

Cloud is a common natural phenomenon in the sky, and has an irregular and arbitrary appearance. Cloud has serious interference with optical sensors, so it is meaningful to research the optical characteristic of cloud. In this paper, lidar was used to measure the vertical atmosphere, and the atmospheric extinction characteristic data were obtained by retrieving the measured data. During the measurement period, clouds appeared in the sky, and it information was recorded. The extinction characteristics of cloud, the height of cloud bottom and the height of cloud top were given, and the transmittance and optical thickness of the cloud were further analyzed.

In order to study the effect of laser backscatter on the laser semi-active seeker, establish a laser backscatter model to analyze the influence of laser backscattering and calculate how much the safety distance(vertical distance between seeker and laser beam) is required correspondingly. Change the angle of view of the seeker, to analyze the influence of backscatter under different field angles. It was found that the larger the field angle is, the stronger the effect of laser backscattering is. By changing the visibility of the atmosphere and analyzing the effects of backscatter on the seeker under different conditions of atmospheric visibility, it was found that the smaller the atmospheric visibility, the stronger the laser backscattering effect. In short, by changing the angle of view of the seeker and atmospheric visibility, the effect of the backscattering phenomenon can be changed and it requires different safety distances to guarantee the safe launch of missiles correspondingly.

We propose here a design of Lyot-Solc composite structure for liquid crystal tunable filter (LCTF) using nematic liquid crystal, which is with high efficiency, narrow bandwidth and electrical tunability. LCTF with high efficiency has many important applications in the fields of optical communication, spectral imaging, and displays. However, most LCTFs adopt cascaded Lyot-type or Solc-type structure, in which multiple pieces of polarizing optical elements exist, causing intensive loss of light intensity. The Lyot-type filter has narrower full width at half maximum (FWHM), but the transmittance is lower. The Solc-type filter has high transmittance and larger free spectral range (FSR) but broader FWHM. We propose a new structure of LCTF composed of Solc-type and Lyot-type structure. The composite 3-levelSolc and 2-level-Lyot LCTF transmission spectrum is a combination of the advantages of the two structures. Through the reasonable structural design, the spectral transmittance is improved, and the secondary transmission peak in the visible spectrum is effectively minimized. At the same time, the output central wavelength can be electrically tunable in the range from 400nm to 650nm by loading different amplitude of driving signals. When the driving signals with amplitude of 1.61V, 1.45V and 1.25V are respectively loaded on the liquid crystal cells of the LCTF, the central wavelengths of the output spectrum are respectively 433nm, 510nm and 595nm, corresponding to the FWHM of 13nm, 16nm and 22nm.

We investigate the conversion of mode locking of bright pulses, dark pulses and dark-bright pulses in an Erbium-doped fiber laser (EDFL) based on a Molybdenum disulfide (MoS2) films saturable absorber (SA) experimentally. When the pump power is 150 mW, by changing the polarization controller (PC) to change the polarization state in the laser cavity， we observed the bright pulse trains, the dark pulse trains and the dark-bright pulses trains in turn. All pulse interval are about 58 ns, and the repetition frequency of pulse is 1.7 MHz. The study provides a method for the conversion among bright pulses, dark pulses and dark-bright pulses.

The photonic lantern is an all-fiber-based linear optical element that couples light efficiently and evolves modes functionally between a set of single-mode waveguide and a multimode waveguide. Our study is based on different core photonic lanterns, which are fabricated by using the ‘ferrule technique’ method, with the single-mode array in a certain geometric arrangement. The process of the light propagation through the lanterns is simulated and the experiments according to the simulation results are conducted. The mode combining and evolution in the 3-core lanterns is simulated to study the necessary conditions for achieving the fundamental mode with good beam quality in large-mode area (LMA) fiber. Appropriate input (the amplitude ratio of each channel is 1:1:1, the phase and polarization state are the same) is injected at the single-mode (SM) end with some random disturbance on amplitude and polarization (the relative change is 20%). The M² factor at the multimode (MM) end has a standard deviation of 0.0001 orders of magnitude. However, the M² factor varies from 1.05 to 2 or even more with the changes of the phase difference at the SM end. Thus, the adaptive optics (AO) technique is used in our experiment, which can adaptively determine the appropriate phase to be applied to the input fibers. In addition, the modes behavior in 6- and 7-core photonic lanterns is simulated to obtain the ideal input (including the amplitude, phase and polarization of each SM channel) for achieving the six lowest order modes output. And these two kinds of photonic lanterns are compared from the aspects of drawing difficulty, mode coupling efficiency, transmission loss, and application feasibility in module multiplexing.

This study was aimed to demonstrate whether laser treatment on dentin is effective to improve the marginal and internal fit of CAD/CAM occlusal veneers, which is a conservative restoration for severe tooth defect from abrasion. Sixteen extracted molars were divided into 4 groups according to adopting laser treatment on dentin and milling materials (n=4): Lava Ultimate CAD/CAM Restorative with no laser treatment on dentin (group LU-C), Lava Ultimate CAD/CAM Restorative with laser treatment on dentin(group LU-L), IPS Empress CAD with no laser treatment on dentin(group IE-C) and IPS Empress CAD with laser treatment on dentin(group IE-L). After the restoration adhesion, all of specimens were scanned by micro-computed tomography(micro CT) to evaluate the marginal and internal fit of each specimen by artificial setting measuring points from both bucco-palatal and mesio-distal direction. For marginal fit, there was no statistical difference with or without laser treatment on dentin for either milling material. For internal fit, the situation was identical. Laser treatment on dentin would not affect the marginal or internal fit of CAD/CAM occlusal veneers, therefore, it may not be necessary for improving the fit of restorations.

In order to widen the spectral coverage of imaging spectrometer based on Acousto-optic tunable filer (AOTF) from 400 nm to 2500 nm, a new configuration of all reflective fore-optics is proposed. The primary and secondary mirrors are used as common objective for visible and short-wave infrared channels, and then there are two independent tertiary mirrors in each channel. This configuration not only solves the problems caused by multi-view observation in traditional systems, but also meets the aperture requirements of both AOTFs to make them work in peak performance. The initial structure parameters is calculated by simultaneous Seidel aberration equations. The final design results validate the availability of this configuration in the AOTF based imaging spectrometer with two channels.

In this paper a method to estimate surface roughness of sand land from multi-angle and multi-waveband polarized detections is presented. Firstly, the polarized bidirectional reflectance distribution function (pBRDF) of the sand land’s surface based on the microfacet theory was established. Then three sand samples with particle sizes of 0.5 mm, 0.7 mm and 1 mm were obtained by a series of sieves. And the polarization information was acquired by full-polarized multispectral imaging system based on Liquid Crystal Variable Retarder (LCVR). We used the nonlinear least squares method to estimate the surface roughness of from the measured data. Lastly, the analysis results show that the accuracy of sand roughness estimation is improved as the number of the angles (i.e., source incident angles and detection angles) and wavebands increase until the estimation accuracy saturates. It is indicated that the method based on polarization imaging detection to estimate sandy land surface roughness is effective.

Metallic nanorod metamaterials, arrays of vertically aligned nanorods embedded in an alumina matrix (diameter ~80 nm, length 100-250 nm, period ~113 nm), have recently emerged as a flexible platform for applications in photonics, opto-electronics and sensing. The optical constants for these nanostructured materials are directly associated with their crystallinity. Controlling the crystallinity of these metamaterials in a fast manner has presented a new challenge. Here we show a laser annealing with a pulsed Nd:YAG laser (λ = 532 nm, FWHM 15 ns) to rapidly change the crystallinity of the metallic nanorods. The small column X-Ray diffraction characterization shows that not only the crystallinity of the metallic nanorods is changed, but also that evaporation of the metal occurs with laser annealing.

As a kind of hollow-core optical waveguide, the optical field can be bound in the core of anti-resonance hollow-core fibers, so it can effectively overcome the ordinary quartz glass absorption loss in the mid-infrared band. In this paper, we use FEM (finite element method) to theoretically calculate the transmission characteristics of a non-node anti-resonance hollow-core fiber over the mid-infrared range of 2-5μm. The influence of the micro-nano structure wall thickness on the transmission spectrum of this novel hollow-core fiber is studied. Simultaneously, the relationship between the wall thickness and the high-loss resonance peak bandwidth is discussed. The results show that the transmission characteristics of this fiber match well with those of ARROW (Anti-Resonant Reflecting Optical Waveguide) model. With the increase of the micro-nano structure wall thickness, the first-order high-loss resonance peak is obviously “red-shifted” and its bandwidth increases linearly. When the wall thickness of the micro-nano structure is about 1μm, the transmission loss of the fiber in the mid-infrared band is small. This work has provided some references for the experimental research on the nonlinear effect of the fiber in the mid-infrared band.

For high power thin disk laser (TDL), the anti-amplified spontaneous emission (ASE) cap is one of the effective methods to suppress the ASE effect. Thermal aberration and dioptric power of the capped disk was stronger than that of the uncapped disk. With a particular anti-ASE cap thickness the dioptric power of the capped disk almost keeps constant with the increase of pump power density. However, the pump spot uniformity of a thin disk laser will be changed if the anti-ASE cap is thick enough. A numerical model developed to analyze the pump spot uniformity for different thickness anti-ASE caps. The analysis results show that the thickness of the anti-ASE cap will deteriorate the pump spot uniformity. Thus, weighing pump spot uniformity will be important for designing an anti-ASE cap (YAG, n=1.82) with an optimal thickness to realize higher-power laser generation.

Azimuthal polarization beam amplification up to an average power of 11.08 W using the Nd:YAG amplifier structure was obtained with the relative purity of 93% at 1 kHz.The beam quality factor M² is 3.29 and the beam wavelength is 1064 nm. The amplification factor of the amplified picosecond azimuthally polarized beam is 207.9%.

In this report, two kinds of ytterbium doped double-cladding fibers (YDFs) are fabricated by Modified Chemical Vapor Deposition (MCVD) in conjunction with solution doping technology. The fiber core contains SiO₂, Yb₂O₃, Al₂O₃, and P₂O₅. After testing in a master oscillator power amplifier (MOPA) configuration, the maximum laser output power of 25μm-core YDF and 30μm-core YDF reaches 3kW and 10kW. In addition, nonlinear effects are not found in the experiment. The experiment results experience that solution doping is a promising technology to fabricate high power laser fiber.

The soft-killing laser weapon plays an important role in photoelectric defense technology. It can be used for photoelectric detection，search，blinding of photoelectric sensor and other devices on fire control and guidance devices, therefore it draws more and more attentions by many scholars. High power fiber-optic laser has many virtues such as small volume, simple structure, nimble handling, high efficiency, qualified light beam, easy thermal management, leading to blinding. Consequently, it may be used as the key device of soft-killing laser weapon. The present study introduced the development of high power fiber–optic laser and its main features. Meanwhile the key technology of large mode area(LMA) optical fiber design , the beam combination technology, double-clad fiber technology and pumping optical coupling technology was stated. The present study is aimed to design high doping LMA fiber, ensure single mode output by increasing core diameter and decrease NA. By means of reducing the spontaneous emission particle absorbed by fiber core and Increasing the power density in the optical fiber, the threshold power of nonlinear effect can increase, and the power of single fiber will be improved. Meantime, high power will be obtained by the beam combination technology. Application prospect of high power fiber laser in photoelectric defense technology was also set forth. Lastly, the present study explored the advantages of high power fiber laser in photoelectric defense technology.

All-solid-state lasers have become one of the most promising research fields in the field of lasers because of their small size, high efficiency and convenient operation. All-solid-state lasers use semiconductor lasers as pump sources, however, Compared with gas lasers, solid-state lasers and fiber lasers, high-power semiconductor lasers have poor beam quality, thus limiting the progress of all-solid-state lasers. Therefore, improving the power and beam quality of semiconductor lasers has become a bottleneck in the development of all-solid-state lasers. The unit beam of the semiconductor laser is rectangular, so the beam needs to be shaped and focused to form a spot before being coupled to the laser medium. Due to its poor quality the spot center has a high optical energy density. When using LD end-pumped mode, the spot can easily destroy the film of the working medium end. In this paper, a uniform function describing the distribution of refractive index and the related parameters were used. And use this function to simulate and calculate the transmission characteristics of optical fiber. Based on the influence of fiber refractive index and core structure on the distribution of optical power in cross section, the homogenization of the LD beam spot is achieved by designing the core structure of optical fiber. This paper established optical fiber transmission model of light waves by using Matlab software and confirmed the influence of the refractive index distribution on the optical power distribution by using Comsol Multiphysics software.

In this manuscript, a 3.53kW average output power all-fiber laser system at 1064nm with 3dB linewidth as narrow as 0.16nm and near single-mode beam quality (M² ≈1.7) is demonstrated. There is no obvious stimulated Brillouin scattering, stimulated Raman scattering or amplified spontaneous emission observed. To the best of our knowledge, this is the highest output power of all-fiber laser system with narrow-linewidth and near single-mode beam quality ever reported.

In this paper, the system performance of free space optical communication of coherent OFDM is studied by the K distribution atmospheric turbulence model under strong turbulent conditions. The channel attenuation model derives the closed form expressions of the outage probability and symbol error rate of the system under the three factors of atmospheric turbulence, path loss and pointing error. The signal mapping method has used QAM. Simulation respectively analyzes the single jump, triple jump and four system mapping, the subcarrier number on order coherent OFDM the interruption of FSO system performance and the influence of the error performance came to the conclusion that the simulation provides a reliable theoretical basis for practical applications.

A dual-wavelength passively mode-locked Yb-doped fiber ring laser with an all-fiber format Sagnac loop as the spectral filters in the all-normal dispersion (ANDi) regime is reported demonstrated. By adjusting the polarization states in the cavity, both the output pulses duration and the central wavelength of mode-locked laser can be changed. The central wavelength of laser output is solely determined by the central wavelength of the channels of the Sagnac loop. It provides a new possibility to achieve an all-fiber format, multiwavelength and mode-locked laser output with the ANDi cavity in a simple and stable manner.

Towed linear array array based on fiber laser hydrophone which had much research potentiality owing to its higher acoustic pressure sensitivity, smaller size and lower difficulty of multiplexing. Flow noise is one of the main sources of noise in the towed linear array system. It will compress the dynamic range of fiber laser hydrophone and reduce the detection ability to small signal. In this paper, the structure of a 4 channel fiber laser hydrophone towed linear array was presented, and the data of sea trial of flow noise was analyzed. The results shows that the influence of flow noise mainly concentrate on the low frequency band which under 500Hz, and the background noise level has increased nearly 70-80dB when the array is towed at the speed of 3 kn.

A linear cavity all normal dispersion Yb-doped fiber laser based on the reflection volume grating and the SESAM(Semiconductor Saturable Absorber Mirror) has been demonstrated. Stable wavelength continuous tuning passively mode-locked laser pulse is obtained at room temperature with the repetition frequency of 16.52MHz. The spectral bandwidth of passively mode-locked pulse is 0.33nm at the central wavelength of 1032nm with the maximum average output power of 10.3mW and the monopulse energy of 0.64nJ. The central wavelength of the mode-locked pulse is tuned in the range of 1011.8~1050.7nm with the tuning range of 38.9nm by rotating the volume grating in taking advantage of its dispersion and wavelength selection characteristic. The fiber laser can be used as the optical source in DWDM/OTDM communication system or OCT system due to its wavelength tuning characteristic.

In the field of measuring the laser power, the traditional way is direct measuring based on thermal effects. In this method, the laser power can be measured from the temperature change of the sensor absorbing the laser light. However, it is difficult to operate when the power exceeds 10kW level because of the linearly scaling size of absorbing object and the relatively long recovery (cooling) periods, which results in the proposal and fast development of indirect measuring technique route. Using light pressure to measure laser power is one of the recent research hotspots of indirect measuring. The typical system design is a scale attached with a nearly perfect mirror that had shown the advantages such as high accuracy, fast response, real-time measuring and convenient calibration. Nevertheless, the commercial mirror (with a reflectivity of 0.997 as a typical value) and scale (with a 100nN resolution as a typical value) cannot achieve a stable measuring due to the feeble light pressure. In fact, the measuring uncertainty could be 7%-13% in practical operation. So it is reasonable and feasible to amplify the light pressure. In this paper, we propose a new structure design based on oscillation cavity which can improve the energy utilization and increase the number of reflections. The force measured by our system is expected to be 50 times more than that imparted by single reflection if the reflectivity of the mirrors installed on the oscillation cavity is larger than 0.99. This novel method can not only achieve higher sensitivity but also retain the advantages of indirect measuring such as fast response, real-time measuring. The resolution ratio could be at the level of 1W using the same scale as the sensor. The theoretical principles and system design will be introduced and analyzed in detail.

In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave(LSAW) induced millisecond multiple pulsed laser on aluminum alloy, made theoretical investigation. And the finite element analysis software, COMSOL Multiphysics, was utilized in the research. we simulated the generation and propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated aluminum alloy irradiated by long pulse laser with 35J energy, 1ms pulse width and 1mm spot radius in the case of different pulse number, we first obtain the simulation result of velocity fields and temperature fields of LSAW, the results showed that there was a certain temperature cumulative effect near target material; Aiming at obtaining the relationship between the generation time of LSAW and laser pulse number. We keep the laser pulse width, energy density and pulse frequency unchanged, the pulse number was 3, 5, 10 respectively; the results showed that the generation time of LSAW become shorter by increasing the laser pulse number. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.

We have made simulations for a 3*1 photonic lantern and the latter experiments were carried out to test characters of the lantern we designed. The three core lantern with 0.004 rad taper angle has a 15 mm taper length which begins with a 125 μm outer diameter and ends with a 10.4 μm outer diameter(core diameter to outer diameter ratio is 2/25), while the NA of single mode fiber is 0.08 and for 25/400 μm core/cladding diameter few mode fiber it is 0.1. In order to obtain preferable LP₀₁ mode shape, we used a phase control system to lock the phase of each channel staying consistent. The consequence demonstrated that the whole phase distribution of single mode fibers was controlled to an extent. Compared to amplitude, photonic lantern is more sensitive to phase fluctuation. We made simulations using Rsoft to test different variables of light propagating in 3*1 photonic lantern, and the results were in agreement with the conclusion. Thus, coherent beam combination based on dithering phase locked technique was studied systematically and we applied it to 3*1 photonic lantern. As a result, the beam received by light spot analyzer showed a stable mode shape but still existing some differences compared to expected LP₀₁ mode or LP₁₁ mode, which put forward reflection about the basic theory inside photonic lanterns (the beam propagating through tapered region didn’t make sense if using coherent beam combination calculation). At last, we attempted to explore the beam propagation through the lantern and to give any better evaluation function in phase control algorithm so as to improve the phase locked process.

Amplification of low-power pulsed single-frequency fiber laser operating at 1064nm has been theoretically investigated. A single-mode Ytterbium doped fiber (YDF) is pumped by a 980nm CW laser. The seed laser has a peak power of 10mW, repetition rate of 65kHz and pulse width of 7ns. Considering the gain of ASE, the optimal length of YDF is around 0.6m when the system operates with the doping concentration of Ytterbium ions of 10²⁶m^-3, core radius of 3μm, numerical aperture of 0.11 and pump power at 0.3W.

In this paper a single frequency thulium doped silica fiber(TDF) laser operating above 2 μm based on cascaded single-mode-multimode-single-mode(SMS) structures incorporating a Sagnac loop was experimentally demonstrated. Based on the theoretical analysis of the transmission properties of the SMS fiber structure and mode selection characteristic of Sagnac loop, two cascaded SMS fiber devices with same multimode fiber lengths around 3.24 cm were used in our laser system to select the specific lasing wavelength above 2 μm as well as enhancing the suppression of lasing around 1900 nm. And 6.5 m unpumped TDF were employed in Sagnac loop as saturable absorber to achieve single frequency operation. Single-longitudinal-mode operation of the fiber laser at 2004.05 nm has been achieved with a signal to noise ratio (SNR) more than 60dB.