This paper analyzes the principle and process of laser detection and scattering interception for typical laser detection instruments, and lists the dominating factors that may affect the ability of laser detection and scattering interception. Based on Mie scattering theory, the calculation model of laser detection scattering interception is established, it can be used to calculate the scattering laser power intercepted by laser detection instruments under different conditions. The dominating factors, such as sensitivity, atmospheric visibility, laser power, laser transmission distance and transmission elevation, are simulated and analyzed with the model to get the influence on laser detection and scattering interception in sequence. According to the simulation results, the relationship curve is drawn, and the changing law of laser detection and scattering interception ability under different factors is obtained. This paper provides a useful technical reference for the configuration and optimization of laser detection instruments in different scenarios.
Single-Photon detection technology is widely focused because of the higher sensitivity of light detection. Laser in the near-infrared region (1.0-1.7μm) has the advantages of high atmospheric transmittance, weak scattering and weak solar background radiation, which is the ideal working band of aerosol remote sensing and three dimensional imaging Light Detection and Ranging system (LiDAR). Comparing with the other Single-Photon detection technology, the InGaAs Avalanche Photo Diode (APD) detector is widely used in LiDAR system because of its single-photon sensitivity and excellent time-resolved performance. With the development of semiconductor technology, InGaAs single-photo avalanche diode (SPAD) arrays detector integrating multiple pixels and time measurement circuits are widely applied owe to the ability of collecting photon information. This paper concludes the development of InGaAs single-photon avalanche diode arrays and introduces some typical applications of InGaAs single photon avalanche diode arrays in imaging, the prospect of the developing for InGaAs single photon avalanche diode arrays is also discussed.
KEYWORDS: Signal to noise ratio, Sensors, Avalanche photodetectors, Imaging systems, Backscatter, Target detection, Signal detection, Modeling and simulation, Receivers
The laser active imaging system is widely focused from all over the world owe to the high resolution of angle, range, velocity, the wide range of velocity measurement, the angle-range-gray-velocity information of target, the finitely ability of anti-stealthy. The laser active imaging system based on high sensitivity Avalanche Photo Diode (APD) detector is the main development direction because of remote imaging distance, simple structure and minimization. However, the performance of the laser active imaging system based on APD is seriously affected by many factors, and the relationships between system’s Signal-to-Noise Ratio (SNR) and influence factors are not further studied. In this paper, the modeling and simulation of SNR for the laser active imaging system based on APD is presented. The theory of the laser active imaging system is shown firstly, and the model is derived by means of deducing laser illuminating according to the principle of laser radar. And then, the sources of noise are analyzed by accurately modeling all noise sources in the detection system, the SNR equation of the laser active imaging system is founded. Finally, the relationships between SNR of system and influence factors such as receive optics aperture and amplification ratio are discussed, and correspondingly the improvement is put forward.
Aiming at the requirements of laser detection radius test and evaluation, based on the Mie scattering theory, combined with the use scene of the laser detection instrument, a calculation model of the laser detection instrument's laser detection scattering interception energy is established. Using this model, the maximum scattering detection radius of the laser detection instrument under a certain irradiation distance is simulated and analyzed, and compared with the direct detection radius under direct conditions, the maximum laser detection radius under different irradiation distances is given. At the same time, a new definition of laser detection distance under scattering conditions is proposed. On the one hand, the above research results can support the accurate evaluation of the detection performance of laser detection instruments, and on the other hand, they can provide technical reference and optimization for laser detection instruments in actual use. The research results will be helpful to achieve better detection effect for laser detection instruments.
Numerical simulation is presented to analyze the influence of nonuniform polarization states on a phase locked laser beams array. Beam propagation factor (BPF) is used to evaluate the quality of the combined beam. For a beams array with different polarization states, SPGD algorithm can be used for modulating the phases of the beams to get higher energy concentration degree at far field. The numerical simulation shows that the BPF of a beams array with nonuniform polarization states is smaller than an ideal beams array with uniform polarization states. The average of BPF value decreases with the increase of array number. SPGD algorithm corrects the polarized component that contains more energy as priority.
The hardware-in-the-loop simulation is widely used in laser semi-active guidance weapon experiments,the authenticity of the laser signal is the key problem in the simulation system.Due to the limitations of the simulation devices, the energy distribution of the jamming laser was uneven.In order to assess the impact of the optical homogeneity,combining the application of simulation,the far-field energy distribution was measured.By optical simulation and actual test,according the receiving optical system entrance pupil,the effect on the beam quality to the simulation result was analyzed. By comparing the different working state between actual condition and hardware-in-the-loop simulation,the output of laser seeker and laser guided weapon trajectory were obtained, the influence of the uneven signal was analyzed.In conclusion it was pointed out that the difference between simulation system and actual system has little influnece on laser jamming. The research is helpful to design and evaluation of laser guided weapon simulation.
Laser communication, designation, and ranging are point to point and have a high degree of specificity, current laser detection, such as laser warning receiver system, could detect the scattering laser from the off-axis distance by scattering track on natural aerosols, which is helpful to locate the laser source. However, the intensity of the scattering laser is extremely weak and affected by many factors, in order to evaluate the detection characteristic, a simplified model of off-axis detection for scattering laser in the lower atmosphere based on the Mie scattering theory is presented in this paper, the performances of the off-axis laser detection in different conditions such as off-axis distance, visibility, incidence angle, and delay time are investigated.
Background sunlight has more or less influence on optical receiver operating in the wild. Laser receiver usually has poor performance in sunlight than designed. The paper’s intention is to test and evaluate the influence of background sunlight on laser receiver by rule and line. The measurement method was studied and measuring system was put up. The outdoor experiments were carried out at plateau. The sensitivity of laser receiver was tested separately at noon and night. The test proves that the sensitivity of laser receiver at noon is down 37.77 per cent, compared with the sensitivity at night. The analytical model of maximum operating distance was founded. With the model, the maximum operating distances at noon and night were calculated. The calculation proves that the maximum operating distances at noon falls more than 12 per cent compared with the distance at night. The test and calculation show that background sunlight has a great influence on performance of laser receiver. It’s very necessary to consider the impact of sunlight when testing, evaluating, and using laser receiver.
The CCD imaging method is usually used in the far-field laser energy density distribution measurement, and the method is simple, reliable. The scattering laser energy density distribution in optical extinctive chambers is one of the most important factors affecting the performance of hardware-in-the-loop simulation system for laser guided weapon because of the weak signal, therefore, how to accurately measure the scattering laser energy density distribution is the key factor to the performance of the laser guided weapon evaluation. In this paper, the method of CCD imaging for scattering laser energy density distribution measurement in optical extinctive chambers was shown. Firstly, the principles and setup of measurement based on CCD imaging method were studied, and the model of scattering laser energy density measurement was simplified under special conditions. And then, the calibration process between the region division and the FOV (field of view) of CCD was described simply, the relationship between the gray value and laser energy density was found. Finally, the scattering laser energy density distribution in optical extinctive chambers was deduced by the measurement of the CCD’s gray value, and measurement errors were also analyzed.
According to laser signal simulation, the advantage of application of tapered multi-mode fiber on laser pulse signal transmission was analyzed. By optical system simulation, the effect on the coupling efficiency of 1.06μm laser pulse signal of different angle was analyzed. By optical experiment, the coupling efficiency and transmission mode of different incident angle and force condition were confirmed. Combining the application of simulation system, with convex lens, frosted glass and optical integrator on the outlet of fiber, the far-field energy distribution was measured. According the receiving optical system entrance pupil, the effect on the beam quality to the simulation result was analyzed. The results showed that the application of tapered multi-mode fiber on laser pulse signal simulation is feasible, and the equipment has been used in the engineering projects.
The laser active imaging system is widely used in night vision, underwater imaging, three-dimension scene imaging and other civilian applications, and the system’s detected range increase greatly comparing with the passive imaging system. In recent years, with rapid development of sensor and laser source technique, the laser range-gated imaging system is achieved based on high peak power pulsed laser and gated intensified CCD(ICCD), and it is well known for its properties such as high suppression of backscatter noise from fog and other obscurants, high resolution, long detection range and direct visualization. However, the performance of the laser range-gated imaging system is seriously affected by many factors, and the relationships between system’s Signal-to-Noise Ratio (SNR) and influence factors are not further elaborated. In this paper, the simulation of SNR for the laser range-gated imaging system is studied. The principle of the laser range-gated imaging system is shown firstly, and the range equation is derived by means of deducing laser illuminating model according to the principle of laser radar and the characters of objects and the detectors. And then, the sources of noise are analyzed by accurately modeling all noise sources in the detection system, the model of SNR for laser range-gated imaging system is established. Finally, the relationships between SNR of system and influence factors such as gating time, laser pulse width and repetition frequency are discussed, and correspondingly the solutions are proposed.
In order to precisely measure dynamic angle of sight for hardware-in-the-loop simulation, a dynamic measurement methodology was established and a set of measurement system was built. The errors and drifts, such as synchronization delay, CCD measurement error and drift, laser spot error on diffuse reflection plane and optics axis drift of laser, were measured and analyzed. First, by analyzing and measuring synchronization time between laser and time of controlling data, an error control method was devised and lowered synchronization delay to 21μs. Then, the relationship between CCD device and laser spot position was calibrated precisely and fitted by two-dimension surface fitting. CCD measurement error and drift were controlled below 0.26mrad. Next, angular resolution was calculated, and laser spot error on diffuse reflection plane was estimated to be 0.065mrad. Finally, optics axis drift of laser was analyzed and measured which did not exceed 0.06mrad. The measurement results indicate that the maximum of errors and drifts of the measurement methodology is less than 0.275mrad. The methodology can satisfy the measurement on dynamic angle of sight of higher precision and lager scale.
Background sunlight effect the technical performance of laser detection system significantly. Analyses and experiments were done to find the degree and regularity of effects of background sunlight on laser detection system. At first, we established the theoretical model of laser detection probability curve. We emulated and analysed the effects on probability curve under different sunlight intensity by the model. Moreover, we got the variation regularity of parameter in probability curve. Secondly, we proposed a prediction method of probability curve, which deduced the detecting parameter from measured data. The method can not only get the probability curve in arbitrary background sunlight by a measured probability curve in typical background sunlight, but also calculate the sensitivity of laser detection systems by probability curve at the specified probability. Thirdly, we measured the probability curves under three types of background sunlight. The illumination conditions in experiments included fine, overcast and night. These three curves can be used as reference to deduce other curves. Using model, method, and measured data mentioned above, we finally finished the analyses and appraisal of the effects of background sunlight on typical laser detection system. The research findings can provide the theoretical reference and technical support for adaptability evaluation of typical laser detection systems in different background sunlight.
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