Dual-phase-shift spherical Fizeau interferometer for reduction of noise due to internally scattered light

Toshiki Kumagai,Kenichi Hibino,Yasunari Nagaike

doi:10.1117/1.oe.56.3.034102

Abstract

Internally scattered light in a Fizeau interferometer is generated from dust, defects, imperfect coating of the optical components, and multiple reflections inside the collimator lens. It produces additional noise fringes in the observed interference image and degrades the repeatability of the phase measurement. A method to reduce the phase measurement error is proposed, in which the test surface is mechanically translated between each phase measurement in addition to an ordinary phase shift of the reference surface. It is shown that a linear combination of several measured phases at different test surface positions can reduce the phase errors caused by the scattered light. The combination can also compensate for the nonuniformity of the phase shift that occurs in spherical tests. A symmetric sampling of the phase measurements can cancel the additional primary spherical aberrations that occur when the test surface is out of the null position of the confocal configuration.

Highlights

Fizeau interferometers with transmission flats or spherical references and mechanical phase shifts are among the most successful commercial optical interferometers and have a measurement repeatability better than 0.1-nm root-meansquares (RMS)
We show that the linear combination of the measured phases from several different object positions can eliminate the phase error caused by the nonuniform phase shift
The noise arising from internal scattering of light by dust, multiple reflections, and imperfect coating of the optical components degrades the measurement repeatability in a Fizeau interferometer

Summary

Introduction

Fizeau interferometers with transmission flats or spherical references and mechanical phase shifts are among the most successful commercial optical interferometers and have a measurement repeatability better than 0.1-nm root-meansquares (RMS). The intensity of a stabilized He–Ne laser source slowly varies periodically; its variation during a single phase measurement of 0.5 s, for example, is almost linear, with a relative amplitude variation of ∼0.17% This variation contributes to the degradation of the repeatability by

Methods

Discussion

Conclusion