Design And Experimental Research Of 5 Times Long Working Distance White Light Interference Microscope Objective

Interferometeric microscope objective is a kind of objective which has two functions of micro magnification and optical path interference by adding interference modules in the structure of the traditional microscopical objective.In order to measure the hemisphere-like surface micromorphology,it is usually required that the interferometeric microscope objective has a long working distance.At present,when the focal distance is 45mm,the longest working distance of the existing 5X interferometric microscope objective is only 9.3mm,which is still limited when doing some measurements.This paper aims to design a 5X interferometric microscope objective which has long working distance.Based on the structures of Mirau type,Linnik type and Michelson type,we analyzed the advantages and disadvantages of the three objectives.The Michelson type structure is selected as the interference cavity structure of 5X interference microscopic objective.Take the aberration and practicality of the microscope objective into consideration,we chose the symmetric doublet with "+--+"type as the structure of 5X microscope objective.We optimize the optical system with the aim to get a long distance and finally obtained the working distance 19.06mm.In this paper,We design a reflective alignment optical path to finish the alignment of the interference microscope objective with the measurement instrument of reflective decenter and ZYGO interferometer.After the development of 5X interferometric microscope objective,we use it to measure the surface roughness of optical spherical surface.As spherical profile is different from the plane surface and it will introduce the surface micromorphology measurement error into the result,we propose a processing method of eliminating spherical aberration.In this method,we use the 5X interferometric microscope objective to measure the optical spherical surface.We can get the curvature radius of optical spherical surface and surface contour information by Fourier transform(FFT)and quadratic polar coordinate transform.Then remove the curvature radius from the surface contour information,we will get relatively accurate surface roughness of the optical spherical surface on the surface roughness calculation.The experimental results show that,the method is effective by comparing with the data of the Taylor-Hobson.