Study On Measurement Of Multi-Wavelength Scattering Parameters For Surface Defects Of Ultra-Smooth Optical Components

Ultra-smooth optical elements are an important part of precision optical instruments,and the performance parameters of the optical elements determine that its precision and application.The partial defects or flaws in the effective aperture of the optical element surface have a serious effect on its optical performance.This paper builds the two surface defect detection systems respectively on the bases of the theory of integral scattering detection and angle-resolved scattering detection.Some experiments are taken to the verification to the defects scratches of the known size and type.Exploring the relation between the scattering rate of the surface defects of the ultra-smooth optics and light sources of different wavelengths.According to the relationship of integral scattering and root mean square roughness,and the relationship of angle-resolved scattering and bidirectional distribution function,the paper designs the integral scattering detection and the angle-resolved scattering detection system respectively.Both of the systems contain optical module,signal acquisition and system control module.Integrating sphere is the core part of the integral scattering detection system,and the Lab VIEW as the data acquisition platform.According to the existed researches in the laboratory,the optimized angle-resolved scattering detection system of this paper mainly collects the strong scattered light signal in the vicinity of the reflected light.The optimized system includes the IV signal conversion module,the data display and the control.interface module.The two detection systems take the theory of the cross-correlation detection,and the lock-in amplifier as the key part of the systems,so that all the two systems can extract signals with high signal-to-noise ratio in the complex background noise,which ensure the stability and accuracy of the achieved data.Herein,the tested samples are high-transparency quartz glass sheet,and the surfaces of these samples are engraved with scratches of the known sizes.The depths and the widths of these scratches respectively are 20×25,25×25,and 30×25μm.This paper uses three light sources with wavelengths of 635,525,and 405nm.The experimental results of the integral scattering detection system shows that the shorter the wavelength of the incident light source,the stronger the scattered light energy of the defect,the greater the scattering rate of the surface defect.The larger the size of the defect scratches of the tested sample,the higher the scattering of the surface defect.For the angle-resolved scattering detection system,the projection of the incident beam of the system on the horizontal plane is perpendicular to the surface scratches of the tested sample.When the incident angles（zenith angle）of the light source respectively are30°,45°,and 60°,exploring the relation between the surface defect scattering rate of the samples and angles.At the same latitude,the experimental results show that the farther the detection position is from the specular reflection light,the smaller the defect scattering rate,and as the incident angle decreases,the surface defect scattering rate increases gradually.The dynamic range of the two detection systems of the paper can reach 10¹²orders of magnitude.The two detection systems of this paper can effectively achieve the scattering rate data of defects of ultra-smooth optical components by theoretical research and the experimental explorations.The findings of this study provide a reference for detecting small defects and achieving the size information of defects indirectly.