This PDF file contains the front matter associated with SPIE Proceedings Volume 13154, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The optical system with variable F-number can simultaneously meet the requirements of sensitivity in wide field of view and the requirements of resolution in narrow field of view, and variable F-number infrared detector is an important part of the optical system. Due to the thermal contact resistance, the temperature of the diaphragms is much higher than that of the cold shield of traditional detector, which means the thermal radiation of the diaphragms would adversely affect the performance of the FPAs. Based on the radiation theory, the effect of thermal radiation of the diaphragms on the performance of FPAs was studied from response signal and NETD, respectively. Furthermore, a MW FPAs and a LW FPAs were calculated by the theory of this paper. The results suggest that the temperature of the diaphragms must be 197K or less if the variation of the performance of the MW FPAs does not exceed 10%. And the temperature of the diaphragms must be 152K or less if the variation of the performance of the LW FPAs does not exceed 10%. The research of this paper has certain guiding significance for the design of Dewar assembly with variable F-number.

Photoacoustic detection has shown excellent performance in measuring the thickness and detecting defects in metal nanofilms. However, during ultrafast photoacoustic detection, signal quality depends on both laser parameters and the physical properties of nanofilms. Therefore, it is important to study how physical processes evolve under different laser parameters to improve signal quality in various film materials. In this study, we have developed a comprehensive physical model that combines the Two-Temperature Model with the acoustic wave generation and detection model. Our numerical results, which are based on a 500-nm AlCu film composed of 95% aluminum and 5% copper, closely align with experimental results, demonstrating the validity of this model. This research offers valuable insights for improving photoacoustic signals in practical applications.

Aiming at the serious non-uniformity of infrared hyperspectral data, a non-uniformity correction method based on spectral channel is proposed.This method not only corrects the non-uniformity of each spectral channel image, but also corrects the non-uniformity between spectral channels. By comparing the traditional two-point correction method with the proposed method in this paper, it shows that the method proposed in this paper can not only effectively remove the non-uniformity of each spectral image, but also retain the original spectral curve characteristics of the target, which verifies the effectiveness of the proposed method in this paper.

Based on uncooled infrared microbolometer focal plane array technology, an uncooled THz microbolometer detector with 25um pixel pitch and 160×120 array size was developed. The CTIA read-out integrated circuit was designed and manufactured with 0.25um standard CMOS process. The resonant cavity height of the micro-bridge pixel was increased from about 1.5um to about 23um to enhance the absorption in the THz wavelengthes. The increased resonant cavity height was realized with tungsten plug and CMP process above the aluminum reflector. The THz detector was packaged with ceramic hermetic package, a parylene coating was developed on high resistivity silicon window to increase the THz transmission. The developed THz detector was applied in beam profiling of QCL, LN crystal sources etc.

Avalanche photodiodes (APD) can amplify the photoelectric signal based on the avalanche multiplication effect of carrier to improve the sensitivity of detection. They have the characteristics of low noise and high gain, so they are suitable for long-distance optical communication. In this work, a multi-stage avalanche photodiode structure with SAGCM (Separated Absorption, Grading, Charge and Multiplication region) is proposed based on Impact Ionization Engineering (I²E). The photocurrent, dark current, electric field, gain and noise characteristics of InGaAs/InAlAs avalanche photodiodes are studied by optimizing the grading layer's thickness and doping concentration. According to the final simulation results, the optimized avalanche photodiodes has low excess noise. At 60 V voltage and 300 K temperature, the noise factor k value (the ratio of impact ionization coefficients) of the five-stage APD is 0.012, and the gain can reach 430.

When the space optical remote sensing system works in orbit, it is easy to be affected by the external environment such as vibration and shock, space environment and optical system itself. In this case, the position of the secondary mirror relative to the primary mirror will shift, which causes wavefront aberrations and deteriorates the image quality. The traditional position errors detection technique has the following disadvantages such as complex device, time-consuming calculation, low accuracy and small dynamic range. In view of the shortcomings of the existing secondary mirror position errors detection technology, a large dynamic range secondary mirror position errors detection method based on two-branch convolutional neural network (CNN) is proposed. Taking the coaxial three-mirror system as the research object, its maximum RMS value of offset wavefront aberration is above 6 λ. This method uses a new dual-branch CNN to establish the nonlinear relationship between symmetrical defocus point spread function (PSF) and the secondary mirror position offset under a single field of view, which improves the dynamic range of secondary mirror position errors detection. The prediction effects of the network trained with different fields of view data are compared, and the effects of field deviation and environmental noise on the prediction accuracy of the network are analyzed. The simulation results show that the proposed method can effectively improve the dynamic range of secondary mirror position errors detection, also has high sensing accuracy, and has good generalization ability.

The photomodulated optical reflectance (PMOR) technology has shown excellent performance in measuring the sample’s doping profile and annealing uniformity after ion implantation. However, during PMOR detection, the physical process of interaction between laser and material can be quite complex. Therefore, it is significant to study a complete physical model of ion implantation measurement for the measurement accuracy of the doping profile. In this study, we have developed a comprehensive physical model that combines physical models for the generation and detection of excess carriers and excess temperature. For the samples with the same doping concentration and different junction depths, the finite element simulation results can distinguish three different doping profiles, which verifies the feasibility of the model in monitoring the doping profile. This study provides theoretical support for the measurement of the doping profile after ion implantation.

The event camera is a novel type of bio-inspired vision sensor inspired by the biological retina. Compared to traditional frame-based cameras, it offers high temporal resolution, high dynamic range, reduced redundancy, and lower transmission bandwidth. These unique features pave the way for innovative solutions in the field of computer vision. However, the heightened sensitivity of event cameras to fluctuations in brightness, along with their susceptibility to environmental factors and hardware limitations, presents a significant challenge. It involves capturing spatiotemporal information from the target signal simultaneously with the generation of a substantial volume of noise events. In applications relying on event cameras, this noise compromises target detection precision. Therefore, event stream denoising is essential before further applications can be pursued. Unfortunately, conventional frame-based algorithms are ill-suited for processing event data due to the distinct format of event cameras. In response to the challenges of event stream denoising, using the event stream generated by Celex-V as an example, this paper categorizes noise events and conducts an analysis of the event noise distribution model. Leveraging the characteristics of noise events, such as randomness and isolation, the paper proposes an event-based cascaded noise processing method. This method involves analyzing events in the spatiotemporal vicinity of arriving events and removing noise events from the event stream data. While ensuring the integrity of data flow information, it achieves rapid and efficient noise removal. The denoised event stream is advantageous for subsequent processing in various applications based on event cameras.

In order to improve the calculation accuracy of multialkali photocathode image intensifier’s modulation transfer function, base on the modulation transfer function model of proximity focusing structure. Collecting the modulation transfer function data of image intensifiers that having different cathode types, different cathode materials’ escape equivalent initial potential of photoelectron how to affect modulation transfer function is explored. The modulation transfer function model is optimized on the strength of cathode material characteristic parameter. The results show that in view of the difference between the cathode material characteristic parameters, the SSE between the calculated value of modulation transfer function optimized model and the measured value is less than 6, especially in the high spatial frequency region. The results have theoretical significance for further improving the resolution of high performance image intensifier.

The nanopore-structure YBa₂Cu₃O₇ (YBCO) high-temperature superconducting detectors are novel with their possible phase transition mechanism from insulating to metallic states. In this paper, an array of YBCO nanopore detectors were fabricated and evaluated. Very thin YBCO films were deposited on strontium titanate substrates, and 16×1 high-temperature superconducting detectors were prepared by photolithography, etching and evaporation processes. Connected with the specially designed and developed readout circuit, the detectors were tested in terms of resistance-temperature (R-T) and voltage-current (I-V) characteristics. The R-T curve confirms the insulating phase of the nanopore superconducting YBCO film at low temperature. With increasing the incident intensity of 1550nm light, the resistance of the detector reduces significantly, implying the photoinduced metallic-conduction phase. The photoresponse is detectible under 1550 nm irradiation down to ~10nW, suggesting the possibility of highly sensitive photodetection. Our new devices may have application prospects in many fields such as quantum communication and aerospace detection.

Neuromorphic computing has considerable potential in simulating the efficient information processing capabilities of the human brain. Implementing neuromorphic computing requires the development of artificial synaptic devices that mimic biological synapses, which are the basic for information processing, storage, and transmission in biological neural networks. Herein, we demonstrate a light-stimulated synaptic transistor (LSST) device based on graphene/hexagonal boron nitride (h-BN)/pentacene heterojunction for emulating the basic functions of the human brain. The LSST devices can detect light stimulus at a wavelength of 520 nm and exhibits a variety of typical synaptic properties, such as excitatory postsynaptic current, paired pulse facilitation, and transition from short-term memory to long-term memory. In addition, the LSST device is capable of simulating the learning and forgetting processes of the human brain. Based on the optically and electrically controlled conductivity modulation characteristics of the LSST device, we construct an artificial neural network for perform pattern recognition tasks, and recognition accuracy of handwritten digits is 88.5%. These results mean that our LSST devices have great potential for future applications in neuromorphic computing.

Marine plankton play an irreplaceable role in the marine ecological environment, and it is also an important and popular research field in biology and oceanography. Microscopic imaging system, with the outstanding advantages of high resolution and high magnification, is one of the most direct and effective in situ observation and research tools for marine plankton. To carry out the detection and research of marine plankton more efficiently and reduce the impact of its free movement on in-situ observation, this paper proposes to combine the optical tweezers with the microscopic imaging technology to design a microscopic optical tweezers based underwater in-situ observation system for plankton. The system uses holographic optical tweezers to enable the capturing of plankton in the water body, which allows it positioned stably and imaged clearly within the field of view.

The work described in this paper built a holographic microscopic optical tweezers system in the laboratory and wrote an algorithm for generating phase maps based on diffraction-computed holography, thus break through the limitation that the traditional optical tweezers system can only capture the target at the center of the optical path and realizing free manipulation of targeting plankton in the field of view. Meanwhile, this paper also miniaturizes the laboratory system and completes the design including the underwater chamber and related accessories so that the system can work well underwater. The experiments show that the system can stabilize and image plankton samples well in both static water and flow field, which can meet the requirements of underwater in-situ experiments, indicating that the method has great practical value and application prospects in solving the problem of high-quality in-situ microscopic observation.

In order to measure the underwater flow field, a set of light field imaging system based on microlens array is designed and built based on the principle of light field imaging. The system can continuously sample the flow field of tracer particles, and the obtained images can expand the depth of field through digital refocusing calculation, restore the imaging situation of each focal plane, and extract the focal particles. At the same time, particle image velocimetry is used to calculate the detected flow field, and the flow field results are obtained. The system combines light field technology with microscopic imaging technology to track small particles and expand the depth of field. Its light path and structure design are simple and reliable, and can be used in the development of underwater in-situ detection instruments.

This article reports a multi-gain-stage avalanche photodiode based on InGaAs/InAlAs superlattice, which has much higher gain and signal-to-noise ratio than conventional APD. The physical mechanism of high gain and low noise of this type of APD is analyzed in detail, and the dead space gain theory (DSMT) is introduced and applied to the calculation of the excess noise factor of multi-gain-stage APD. For a 5-stage device, the distribution of electric field and carrier dead space is calculated, and the ionization rates before and after considering phonon scattering are compared. The gain vs excess noise factor curve is obtained and compared with the traditional McIntyre model. The simulation results shows that the excess noise factor is equivalent to the McIntyre model k=0.049. Based on the simulation results, an optimized epitaxial material structure is designed, Front-illuminated photo diode were etched in the molecular beam epitaxy (MBE)-grown epitaxial material, the mesa sidewalls were encapsulated with Si₃N₄ . The test results of a 50μm diameter device are as follows: maximum above 1000, excess noise factor of 2.39@M=100, spectral response range of 0.95~1.65μm, response time of 1.26ns.

The nonlinear effect is one of the characteristics of photodetectors. In infrared measurement systems, photodetectors like MCT, InGaAs and InSb are widely used; while their non-linearity is still a problem. National Institute of Metrology, China has built an infrared spectral radiance measurement system. The system consists of a variable temperature blackbody as the standard radiation source; and uses a Fourier transform Infrared Spectrometer as the measuring instrument, including a MCT detector which is the main source of non-linearity uncertainty. In this study, an interpolation method and a polynomial fitting method are used to correct the non-linearity of the measurement system. To do so, at first, set the temperature of the standard variable blackbody to a serial of different temperatures, and use the measurement system to acquire the spectral response signal at each temperature; then, calculate the spectral radiance value of the standard radiation source based on the Planck’s law; after that, in the spectral dimension, analyze the relationship between and , and correct its non-linearity with a piecewise linear interpolation method and a multi-order polynomial fitting method; finally, verify the above two methods and analyze the relative deviation accordingly. The results show, the deviation is relatively large in wavelength range smaller than 8μm; while in 8μm~14μm wavelength range, the relative deviation is around 0.5%~0.001% and around 1.0%~0.001% by using the piecewise linear interpolation method and polynomial fitting method, respectively.

Conduit connectors are widely used in the manufacturing of aviation equipment such as aircraft engines and aircraft assemblies. The surface roughness of conduit connector is a key quality characteristic to ensure the sealing connection of pipeline systems. Small deviations in the surface quality of conduits can lead to significant quality issues in aircraft, so high-precision measurement of micro roughness of conduit connector surfaces is of great significance for controlling aircraft quality and optimizing support manufacturing processes. Compared with contact measurement methods, optical measurement methods take an irreplaceable position in micro-nano scale roughness measurement which have many advantages such as non-destructive, high-precision and high-speed. An optical measurement method for surface roughness of aircraft conduit connector based on a triangular structured illumination system is proposed in this article, which combines high-precision fringe phase analysis algorithm and accurate height mapping algorithm to realize morphological restoration and the calculation of the roughness of the tested area. Relational experiment is carried out to verify the feasibility of the proposed method.

In recent years, InGaAs/InP Negative Feedback Avalanche Diodes (NFAD), as a new type of high-sensitivity all-solid- state semiconductor device based on the structure of Single Photon Avalanche Diode (SPAD), integrates a quenching resistor on the SPAD chip. The quenching resistor is integrated on the SPAD chip, which is widely used in photon counting applications such as fluorescence spectrum detection, solar spectrum irradiation, quantum communication, and high-energy radiation monitoring due to its high integration, high sensitivity, fast quenching speed, low after-pulse, and high reliability. In the research, for the high-speed small-signal amplification and extraction, interference and noise suppression, and active-passive hybrid quenching of InGaAs/InP NFAD, a high-speed, low-noise, single-ended differential preamplifier circuit was innovatively used for the amplification and extraction of NFAD avalanche signals, and then a high-speed differential comparator was used for the identification and extraction of the avalanches, and they were quenched by the active-passive hybrid quenching branch, and recovered after a certain delay time. At the same time, the NFAD was reentered into the Geiger state by the recovery branch after a certain delay; meanwhile, the DAC chip containing 14-bit registers was used to realize the high-precision small-step (±1LSB) threshold voltage output to enhance the detector's anti-jamming ability, the input voltage V_DD of DAC was from 2.7V to 5.5V; the circuit can realize the fast quenching and recovery of the NFAD, with a bandwidth close to 1GHz, a quenching time of about 1.23ns, and a dead time of about 0.1μs to 100μs , which met the requirements of free-running-mode photon counting detection.

In recent years, infrared thermal polarization imaging technology has emerged as a new method of infrared detection. Its main objective is to detect, identify, and track the differences in infrared polarization characteristics between targets and scenes. Compared to ordinary infrared imaging systems, this technology offers significant advantages for detecting and identifying man-made targets in complex natural backgrounds. Specifically, the division of focal plane (DoFP) polarimeter is currently being extensively researched due to its compact structure, small volume, and real-time imaging capabilities. However, the focal plane array (FPA) of the DoFP polarimeter exhibits varying response gains and bias parameters, while the micro-polarizer array on its surface suffers manufacturing defects, resulting in significant nonuniformity errors that adversely affect resolution accuracy. This paper analyzes the mechanism behind the generation of non-uniformity in the DoFP polarization imaging system and establishes a relationship between the output grayscale of the system and incident irradiance. Additionally, through the use of a mid-infrared polarization radiation source, the proposed method conducts irradiation calibration and polarization parameter calibration to rectify the non-uniformity of the detection image of the system. Based on experimental results, the calibration model significantly enhances the accuracy of polarization detection information for scene targets.

The segmented planar imaging method is a new imaging concept based on Van Cittert-Zernike theory that offers significantly reduced size, weight, and power consumption replacing traditional refracting/reflecting telescopes with photonic integrated circuits (PICs). As one of the key components, the phase shifter plays a role in compensating for phase, and its phase shift accuracy has an important impact on the imaging quality of segmented planar imaging detectors. In this paper, a degradation model of the accuracy of phase shifters on the degradation of imaging quality is established and the impact of phase shifter accuracy on system imaging quality is analyzed. The tolerance error of phase shifter phase shift accuracy was determined γ≤10% by analyzing the imaging results of spectral channels corresponding to different paired baselines under the same phase shifter phase shift accuracy. The analysis conclusion provides a theoretical basis for the manufacturing of segmented planar imaging detector.

This article mainly studies the current voltage (IV) characteristics of Quantum Well Infrared Photo-detectors, especially the influence of temperature on their performance, as well as the characteristics related to photocurrent and dark current. We measured the IV curves at different temperatures and conducted comparative studies to reveal the differences in the behavior of quantum well devices under photoexcitation and non photoexcitation conditions, in order to gain a deeper understanding of their performance characteristics. Finally, we investigated the response of quantum well devices to different blackbody temperatures and fitted the dark current using the IV curve, which was compared with the actual measured dark current. The results show that the fitted dark current is slightly larger than the actual measured dark current. Through these studies, we can comprehensively understand the IV characteristics of quantum well devices under different temperature and lighting conditions, providing strong support for their optimization and control in various applications. These research results are of great significance for the design and engineering applications of QWIP.

Cuffless and continuous estimation of blood pressure can be achieved by using photoplethysmography (PPG) signals and neural networks. This approach offers an improvement over the inconvenience of operating commonly used cuffed electronic sphygmomanometers which are unable to provide continuous readings. The research aims to identify more suitable network models for the task of blood pressure estimation using PPG signals. Four network models for time-series signals were selected for this study, including recurrent neural network, long and short term memory (LSTM), and gated recurrent unit, which have previously been used for blood pressure estimation with PPG signals in existing studies, as well as a newer network structure, a temporal convolutional network (TCN). PPG signals and blood pressure data obtained from the intensive care medical information set were used as a sample set for evaluating the network's performance. The 61 features with the highest correlation from the PPG waveform feature set were selected as input feature vectors. The findings indicate that LSTM and TCN exhibit high accuracy and can serve as the foundational model for measuring blood pressure. TCN obtains equivalent precision to LSTM, despite a substantially smaller network size. Additionally, the former technique has a greater probability of attaining ongoing blood pressure readings without the need for cuffs.

A phase demodulation algorithm based on the fast Fourier transform (FFT) extrinsic Fabry-Perot interferometer (EFPI) is proposed in this paper. The EFPI is usually of low reflectivity at the fiber end face, and the optical model is simplified as two-beam interference. For fiber optic sensors, the signal information is mainly concentrated in a few spatial frequencies. The proposed phase demodulation method uses a variable step-size fast Fourier transform (VFFT) to accurately extract phase changes. The FFT demodulation algorithm uses data from the entire interference spectrum to calculate the phase at intrinsic spatial frequencies. The VFFT phase demodulation algorithm considers the problem of nonperiodic sampling under different initial cavity length conditions. The signal demodulation performance is simulated and analyzed to verify the reliability of the proposed demodulation algorithm. The results show that the demodulation precision of the VFFT is higher, and the adaptability to the same cavity length and reflectivity is better than that of the FFT. From the perspective of engineering practice, the demodulation algorithm has more stable performance and provides more technical support for the realization of ocean detection.

Quantum well infrared photodetectors (QWIPs) have natural advantages, such as high material maturity and good uniformity. But its low quantum efficiency is often criticized as a drawback. The quantum well optical coupling structure is one of the key factors affecting the quantum efficiency of quantum well detectors. This article mainly focuses on the impact of the optical coupling structure of quantum well detectors on detector wavelength, coupling efficiency, and other aspects. We have established an optical coupling structure model for quantum well detectors, mainly consisting of three different angles of structure structures: 45 degrees, 62 degrees, and 90 degrees periodic two-dimensional diffraction gratings. The 3D-FDTD simulation method was used to simulate the optical coupling structure of quantum well detectors, and the performance indicators of the three structures, such as response wavelength and coupling efficiency, were compared. At the same time, simulations were conducted on different angles of periodic two-dimensional diffraction gratings. It can be seen that as the grating angle increases, the response spectrum width widens, but the amplitude of the response decreases.

Atmospheric coherence length represents the diffraction limit of light wave propagation through atmospheric turbulence, which characterises the integrated optical turbulence intensity in the atmospheric transmission path of light waves, and the measurement of atmospheric coherence length is of great significance. A light column turbulence lidar for atmospheric coherence length measurements has been developed based on differential image motion method and oblique range imaging for laser light column, which can obtain atmospheric coherence length profiles at a certain height in the vertical direction with a high spatial resolution, and can overcome the problem of non-active turbulence measurement devices that are not able to measure without suitable beacons or beacons that are occluded. The basic principle and system structure of differential light column lidar are introduced, and the whole lidar system can be divided into laser transmitting unit, signal receiving unit and control unit. The laser transmitter unit adjusts the direction of laser emission through the reflector, CCD camera, diaphragm and stepper motor. The signal receiving unit receives the beam backward scattering signals through the telescope and CCD camera to obtain the light column image, and adjusts the position of the CCD camera through the stepper motor to achieve focusing. The control unit receives and sends signals to control the operation of the entire system. A preliminary detection experiment was carried out with this lidar, and the height distribution profile of atmospheric coherence length was obtained. The variation trend of atmospheric coherence length with altitude is consistent with the theoretical trend, which verified the functionality of the lidar system.

The dynamic range of infrared imaging system is one of the important parameters representing its measurement capability. Extending the dynamic range of infrared imaging system can effectively improve its measurement capability for complex scenes, rapidly changing targets, and more. To improve the dynamic range, firstly, the corresponding relationship between the integration time and dynamic range of infrared imaging system was obtained through radiation calibration experiments, and a non-uniform correction method that adapted to dynamic integration time was proposed. On the basis, a large dynamic range algorithm for infrared imaging systems based on multiple integration times was proposed and the algorithm flowchart was provided. For the same scene, this method utilizes different integration times to collect multiple frames of images and perform image fusion and radiometric calibration parameter fusion, which not only obtains high dynamic range of images but also ensures radiometric measurement accuracy. Lastly, using different temperature blackbodies to construct multi-target complex scenes in the laboratory, and multiple sets of blackbody target images were obtained using an infrared camera and measurement error analysis was conducted, and through processing, high dynamic range images were obtained, the algorithm's effectiveness was verified. The experimental results showed that the algorithm can effectively improve the dynamic range of infrared imaging system, with radiation measurement errors less than 1.5%, at the same time, the high dynamic range images contain more detailed information compared to the unprocessed infrared images, which is more conducive to target detection and recognition, and can meet the measurement application of infrared target characteristics. With the improvement of the frame rate of infrared imaging system, the method can be applied to various research applications such as combustion process analysis, aerodynamic heating analysis, etc.

A new method of suppressing the fading effect of phase-sensitive optical domain-of-view reflectometer (Φ-OTDR) by using a phase-modulated frequency comb is presented in this paper. The distribution of fading points is different, so frequency division multiplexing (FDM) radiation can be used to suppress the fading effect. In the experimental system of this paper, firstly, frequency comb continuous light is generated by phase modulation; Then, different Rayleigh backscattering (RBS) intensity distributions are generated by pulse detection light modulating and injecting into the sensing fiber. Finally, the intensity distribution of RBS is extracted by amplitude estimation method. The phase is processed to eliminate the missing truth. The fading suppression is realized by our system, and the suppression effect is evaluated. By using a constant amplitude optical frequency comb with seven frequency components, the fading probability of the system is drastically reduced from 5.49%-9.83% to 0.08%. The method proposed in this paper has larger modulation bandwidth and more flexible frequency combination scheme, which can better suppress the fading effect. This method does not sacrifice the response bandwidth of the system, and can accurately control the phase delay, so it is very helpful to fully suppress the fading effect.

As a typical representative of new hybrid photodetector, electron bombardment active pixel sensors (EBAPS) not only have the advantages of high sensitivity, fast response and wide spectrum of vacuum devices, but also have the advantages of high spatial resolution, low power consumption, low cost, mature technology and digital output of solid-state devices which have become the mainstream research direction of digital night vision devices at present. EBAPS devices based on third-generation cathode material gallium arsenide (GaAs) exhibit higher cathode sensitivity and quantum efficiency in the near-infrared band. They have addressed cathode fatigue issues through automatic gating high-voltage power supply technology, effectively improving cathode resolution and dynamic range. This paper introduces the research status of digital low light level (LLL) devices, focuses on the research progress of EBAPS devices based on GaAs cathode, and puts forward the prospect of digital low light level devices for night vision in the future.

In this paper, a novel chlorophyll measurement system based on Y-type fiber is designed, and the chlorophyll value is obtained according to the intensity ratio of laser fluorescence-Raman signal produced by laser incident into water. In the system, a 405nm semiconductor laser is used as the light source. The laser is coupled into the delivering port of Y-type fiber and then transmitted into water. The generated scattered light, water Raman light and corresponding fluorescence are received and transmitted into spectrometer through the detecting port of Y-type fiber, and the chlorophyll can be obtained by analyzing the laser fluorescence-Raman ratio of water spectra. In experiment, we detect the chlorophyll standard solutions under a range of concentrations, and establish the correlation between chlorophyll concentration and fluorescence-Raman ratio (r²=0.98). In addition, the chlorophyll of natural water sample is measured with laser spectroscopy, the results of which are consistent with chlorophyll values obtained by traditional spectrophotometry. The experimental results prove that the chlorophyll detection method proposed in this paper has the advantages of high sensitivity, high precision, high detection speed and simplicity, which can be widely used in various water areas for real-time chlorophyll detection.