The Application Of Phase Detection Technique Used In The Ultra-Precision Surface Flatness Measurement

Abstract

A series of equi-thickness interference fringes will be produced by the paired-optical testing plates in a Fizeau interferometer. The paired-plates are also formed a structural part of the interferometer. The variation of the light intensity distribution of these fringes will character the relative flatness of two plates in pairing, therefore, one can accurately measure the flatness of the above mentioned plates if a detector is used to scan the light intensity distribution on some certain points of these interference fringes. These points will display the error of the testing surface effectively and sensitively. That is the principle used to measure the ultra-precision plane in this paper. The authors had been developing this principle and suggested a corresponding device and its practicable operation, as well as the discussion about the theoretical accuracy and optimal measuring condition was done. According to the experimental divice, the obtainable relative flatness resolution of two plates in pairing is better than λ/1000. The absolute error of one plate from relative measurements also could be obtained after a special calculating if necessary.