In recent years, Low-Light-Level (LLL) remote -sensing camera has become a novel subject for the development of aerospace optical remote-sensing payloads. LLL remote sensing camera works in ultra-low light conditions, the image signal is very weak and requires image intensified technology to achieve. In order to make better use of LLL remote sensing data, it is necessary to establish the quantitative relationship between the amount of radiation received by the camera and the digital signal output to process the image. That's radiation calibration technology. Therefore, the radiation calibration of the LLL remote sensing camera is particularly important. In this article, first the requirements for calibration of LLL remote sensing cameras are analyzed in theory. After that, a radiation calibration scheme of the LLL remote sensing camera is put forward. Finally, the radiation calibration test is carried out, and the calibration data are analyzed. The results show that the calibration scheme of LLL remote sensing camera is reasonable and feasible.
The surface contribution analysis method is to find the wavefront map at the local intermediate entrance and exit pupil reference spheres for each optical surface. Direct pictures of each surface aberration contribution are then given by fitting the wavefront errors with Fringe Zernike polynomials which can help optical designers to find the origins of the main aberrations at the final focal plane and make them choose the effective variables for optimization consciously, which is very helpful for designing the freeform optical system with hundrands of variables. This paper discusses the surface contribution analysis method. A Matlab routine is written to communicate with Code V and to give direct pictures of aberration contribution for each surface. A compact freeform optical system is designed to validate the surface contribution analysis design method which is proved to have good convergence and very directive for optical designers.
The 470mm lightweight primary mirror of a space telescope is made of ULE, and supported on a titanium hexapod. The hexapod consists of six bond pads, six titanium struts with flexures and three support parts. The hexapod provides a quasi-kinematic mount for the lightweight mirror, and the flexures are used to isolate optical elements from the mechanical and thermal deformations of the support structure, then the surface figure distortion of the mirror is minimized. In this paper, the finite element method is used to analyze the static and dynamic characteristics of the mirror assembly. Then, six pads are bonded to the mirror and the support hexapod is assembly. The vertical optical test of the primary mirror assembly is implemented. Vibration test of the mirror assembly is performed, and the test results are consistent with the results of the finite element analysis.
The manufacturing and testing of a surface modified silicon carbide mirror with a bowl-shaped structure was introduced. The entire process flow includes pre-modification silicon carbide substrate processing, silicon carbide substrate surface modification, and silicon modified layer processing. Firstly, before the modification, the conventional processing method of silicon carbide was used, and the effect of the support form on the figure was eliminated by multiple direction rotation testing.At the same time, the self-aligned compensation cross-test was completed and the accuracy of the aspherical surface coefficient was verified. In addition, the polishing process of the silicon modified layer material was studied, and the optimum process parameters suitable for polishing the silicon modified layer material were found out. Based on the above experiments, the modified optical processing adopts a combination of two kinds of polishing technology: flexible chemical mechanical polishing (FCMP)and ion beam figuring (IBF).The surface roughness and surface finish of silicon modified layer are improved by flexible chemical mechanical polishing technology. The high figure accuracy of silicon modified layer is achieved finally by ion beam figuring technology. Finally, the final result of the mirror after IBF is:the RMS values of the figure and roughness in the Φ450 mm aperture is 0.01λ (λ=632.8 nm) and 0.52 nm. The mirror's processing results fully meet the design specifications.
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