Compared with conventional optical satellites, ZY-3(03) has its outstanding advantage in the combination of camera stereo observation and laser altimeter to directly obtain elevation control points, which can provide high-precision data for real three-dimensional China construction, geographic national conditions monitoring, farmland protection, geological disaster prevention, etc. In order to meet the demand of laser altimeter that the divergence angle is less than 0.1mrad, a laser beam expanding system is developed. The optical system with Galileo structure is composed of a negative lens group and a positive lens. Through the adjustment of the lens spacing and centering adjustment, the installation and adjustment of the beam expanding system under normal pressure is completed, and the wave-front error, defocusing and magnification are tested. In order to meet the conditions of vacuum use, vacuum presets are performed by adjusting the spacing between the front and rear lens groups. The vacuum divergence test of the transmitting system is carried out together with the laser. The measured divergence angle of the transmitting system is 0.084mrad, which meet the system design requirements. Subsequently, a mechanical environment test and a thermal vacuum environment test are carried out. The divergence angles before and after the tests, during the high and low temperature conditions are stable and are all less than 0.1mrad.
To investigate the distribution characteristics of subsurface damage in fused silica, three different machining methods - cutting, grinding and lapping were adopted. The method of combination of step-by-step polishing and wet etching were applied to expose the subsurface damage and their distribution characteristics in horizontal and vertical directions were analyzed and compared. Experiment results showed that the numbers of subsurface cracks induced by different processes have similar exponential distribution in depth, although their maximum depths were varied with machining methods. Most of the cracks, more than 90%, distribute within half of the maximum crack depth, while only a few cracks extend deeper and contribute the maximum SSD depth. The ratio of SSD depth to Rz for lapping, slicing and grinding based on our work are about 1.4, 1.8 and 2.8, respectively. The present results indicate a nonlinear correlation between SSD depth and Rz.
Fiber optic assemblies which are more flexible, highly efficient, high reliability, small mass and volume have been used in several spaceborne laser altimeter systems for laser sample, laser monitor, echo signal receiver and altimeter calibration. Moreover, application procedure and verification plan of commercial fiber optic assemblies used in spaceborne laser altimeter system is proposed. It is useful for fiber optic assembly’s development and qualification.
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