The Large Aperture Optics Through Reflectivity Measurement System

It is a difficult task to measure the reflectance, transmittance and optical uniformity of an optical coating with very large aperture. In this dissertation, an automatic near-UV/VIS/NIR(340-1060nm) spectrophotometer which has the character of multifunctional and high precision has been developed for spectrum analysis of optical coatings on very large aperture optical elements. It can give two-dimensional scanning result of a sample with substrate surface size of 600mm*350mm and 70mm thickness. The testing beam can be s- or p-polarized, at an incident angle from 0° to 70°.Firstly, the theoretical design of the reflectance, transmittance and optical uniformity of an optical coating with very large aperture is analyzed and presented. Also, the method of correlation detection is adopted to measure the weak signal in this measurement system.Secondly, the scanning technology of the large aperture and board incident angle with high precision has been well researched. And the compensate method of the longitudinal displacement by adjusting the direction of entrance hole on the integrating sphere has been developed.Then, the principle and method of the instrument design has been described. The equipment is composed of optical system, mechanical structure, photo-translating module and computer software system. The performance and character of optical units such as collection lens, filter, modulation disk, monochromator, fiber and polarized prism are discussed; the realization of the scanning structure and design of the sample compartment are given; the process of the automation and circuit of the photo-translating are introduced; and interface and each processing module of the computer software is presented.In this paper, we also do some researches in the automatic spectrum measurement system, such as avoiding the polarization in the fiber, using the devicewith the large photoconductive surface to measure the weak light signal and the calibration means and technology of the base plane in the sample compartment. The systematic and random sources of error have been analyzed as well as the photometric accuracy has been checked. In the near-UV/VIS/NIR region, the wavelength scale is accurate to be within 0.4nm and the overall photometric accuracy can get 0.5% for transmittance and reflectance.At the end of the dissertation, the whole work is summarized and the orientation to improve the performance of measurement system is discussed briefly.