Two-wavelength laser interferometry using super-heterodyne detection

TLDR: In this paper, a super-heterod e detection method was proposed to make high resolution measurements at 241 -I effective difference wavelengths Λ = λ 1 λ 2λ 1- shorter than 30 cm, without being obliged to have interferometric stability at the optical wavelengths Xi and 1.

Abstract: Two-wavelength interferometry is well known since years and often used for ranging and contouring at reduced sensitivity 1. Recently, two-wavelength heterodyne interferometry has been reported, which can be applied for both, smooth and rough surfaces 2. However, this method is limited to large wavelength differences, which can be optically separated (prism, grating). By the availability of tunable diode-lasers as light sources, multiple wavelength interferometry with small wavelength differences is getting increased practical interest 3. It is the purpose of this paper to present a novel method, based on super-heterod e detection, which allows to make high resolution measurements at 241-- I effective difference wavelengths Λ = λ1 λ2λ1- shorter than 30 cm, without being obliged to have interferometric stability at the optical wavelengths Xi and1. itse and to separate these wavelengths optically. This is of great importance for range finding and industrial distance measuring with submillimeter resolution.