Research On Slm Synchronized Scanning Technique Of Laser Range-gated Imaging

Optical imaging is the most common techniques to observe and monitor the target scene,but it is often affected by light absorption and scattering in the light transmission medium such as smoke or underwater environment,especially the scattering,which leads to the optical image signal attenuation and image contrast decline,making difficult to identify targets.All kinds of optical imaging methods to overcome the scattering effect have always been designed and studied,but there is still plenty of room for technological improvement and development.In this paper,the scanning technology of range-gated imaging in the scattering environment is studied to achieve better anti-scattering performance and costeffective in the imaging system.In a high scattering indoor environment formed by artificial smoke,a high-speed photomultiplier tube(PMT)was used to measure the dynamic time course of the pulsed laser beam from emission to scattering and target reflection.The distribution of scattered light in time and space is analyzed.According to the principle of the projection algorithm that maps the three-dimensional space of optical imaging to the two-dimensional display and its symmetrical relationship with the image plane,designing an imaging scanning scheme that spatial light modulator(SLM)dynamically tracks the laser beam to scan the illumination and receive it at a narrow viewing angle,and the multiple scattering light is shielded more effectively both in time and space.Thus achieve the single PMT non-mechanical scanning imaging,the disadvantages of high noise and high cost of high-speed shutter imageenhancing device ICCD multi-channel plate are avoided,the performance characteristics of ICCD staring imaging and PMT scan receiving are analyzed and evaluated in terms of imaging speed and alleviate scattering influence.At the same time,the FPGA development to the driving laser scanning galvanometer is performed.The pixel area of the image plane where the laser beam emission path is projected onto the SLM was calculated.It is also the area where the laser beam illuminated the target spot may be reflected.Thus,the transparent/opaque areas of the SLM pixel is correctly selected to allow the light directly from the laser beam path to enter the receiver and block scattered light in other directions.An imaging lidar system combining synchronous scanning and range gating is established with the PMT receiver.Using narrow beam illumination light for each target point in scanning imaging,the dynamic process of scattered light and target reflected light are detected by a single detector,and looking for targets and it's the time coordinate in this process of the reflected wave,as the grey value of two-dimensional imaging or three-dimensional imaging distance,which reaches about 7times attenuation length imaging visual range.Although the scanning imaging speed of this system is slower than staring range-gated imaging system,it also has the following advantages:(1)The intensity of narrow beam illumination is higher than the large divergence angle beam,and the light received by each pixel is not mixed with the scattered light of subbeams from surrounding pixels;(2)Compared with the ICCD high-speed shutter gate with pre-determined opening/closing time in staring imaging,determine the reflection echo of each pixel on the time axis through the laser emission?scattering and the target reflection dynamic process,this method has greater adaptability to detect unknown targets in different distance ranges.Therefore,the scanning lidar established by the experimental research in this paper has certain advantages in anti-scattering performance and cost performance and so on,to provide a unique technical solution in the wide range of civil and military application fields such as remote sensing,aviation,safe driving and underwater target detection.