Receiving Optical System Design Of Spaceborne Lidar Based On Off-axis Three-mirror Structure

Spaceborne lidar is a kind of product of high precision earth detection technology,which takes the satellite as the platform,it has the advantages of high orbit,a wide range of observation,fast observation speed,little influence on ground and sky background,and has high resolution and high sensitivity.It also plays an important role in measuring vertical distribution of vegetation,sea surface height,vertical distribution of clouds and aerosols,and monitoring of special climatic phenomena.The spaceborne lidar has a great application value because its emergence has accelerated the transformation of Marine science and technology into real productivity.The article has studied and designed a large-diameter off-axis three-mirror receiving optical system for water signal reception,using spaceborne lidar as the carrier.In order to achieve a variety of marine detection requirements,the article has completed the calculation of the optical parameters of receiving optical system of the spaceborne lidar with an on-orbit height of 463 km,and designed the off-axis three-mirror telescopic receiving system,collimation and multi-channel beam-splitting system.The design has obtained a largeaperture off-axis three-mirror optical system with an effective focal length of 1000 mm and a F-number of 1.On the basis of the initial structure of coaxial three-mirror,the central obstruction is eliminated by the way of the diaphragm off-axis.After optimization,the maximum radius of RMS of each field of view spot diagram is only 18.523?m,which meets the design requirements.At the same time,the article has completed the design of the collimation optical system and beam-splitting optical system after the off-axis three-mirror optical system,which are based on the requirements of various applications such as chlorophyll concentration inversion.The collimation system has a focal length of 50 mm,the relative aperture is 1:1.06,and the divergence angle of the parallel beam is only 0.179°.The collimation system is received by 7 optical channels and respectively imaging on the respective unit detectors.In the full field of view range,the spot received by the focal plane of each optical channels is far less than the receiving plane element of the unit detector.After the image quality evaluation and tolerance analysis of the combined optical system,it is proved that the whole system has a better light energy reception rate and can meet the demand of receiving weak echo signals.The article completes the spatial layout design of optical elements,introduces the signal acquisition application of each optical path in the system,and simulates the number of photons for the echo signal.The entire optical system has reasonable layout and high space utilization rate,which is of certain reference value to the development of spaceborne lidar.