Research On Three-dimensional Shape Measurement Technology Of Surface Defects Of Optical Components Based On Digital Holography

The surface quality of optical components has a great influence on high power laser facilities,so the research of microstructure measuring technique of surface defects is needed.This research is helpful to judge the damage degree of the emerging wavefront,and it is of great significance to ensure the laser system security running.Image-plane digital holographic microscopy(IPDHM)is a kind of digital holography,which has the characteristic of high resolution,and in this paper,IPDHM is used to measuring three-dimensional microstructure of optics surface defects.Another characteristic of IPDHM is small field of view(FOV).The theoretical analysis and experimental researches for synthetic aperture digital holography are carried out to overcome this problem.The main completed research work and the achieved results are as following:1.By theoretically analyze the recording principle of holograms of Fresnel digital holography,lens-less Fourier transform digital holography,pre-magnification digital holography and image plane digital holography,the influencing factors of reconstructed image resolution of these four kinds of digital holography are given by this paper,and a conclusion is drawn that resolution of IPDHM is higher than others three under certain condition.2.The experimental system based on IPDHM has been designed and built to measure the microstructure of optical elements' surface defects.There are a few factors which will reduce the quality of reconstructed image,and then some methods introduced to reduce their influence.First,the zero-order image and the conjugate image are separated from reconstructed image.Secondly,the title phase distribution introduced by off-axis recording method is compensated.Third,an accurate calculation method of image plane sampling distance is presented.Fourth,a technique of phase correction introduced which is contributive to eliminate the system error.Some optics with defects have been taken as measuring sample,and the measuring results shows that the error rate is less than 1%.So it proves that this measuring method is valid and accurate.3.By using IPDHM,the optical elements with two sides of defective surface can be detected by once,that will elevate detect efficiency.In order to obtain high resolution measuring results in detection of both sides of optics,a numerical relationship between position of optics and reconstructed image resolution is presented in this paper.4.By using synthetic aperture digital holography,the FOV of measurement is enlarged.Considering that the characteristics of optics'surface defects,a stitching method of phase image is proposed to achieve large area measurement,and it will not reduce accuracy of detection.5.In the research of synthetic aperture digital holography,the causes of producing the misfocus aberration is analyzed,and then a correction method is presented.By experiment research,the correction results prove that this method is verified.In summary,a novel measuring method based on image-plane digital holographic microscopy is proposed in this paper,for the purpose of realizing 3D microstructure measurement of defects on optical surface.Simultaneously,by using synthetic aperture digital holography,the measuring field is enlarged effectively.