Heterodyne absolute distance interferometer with a dual-mode HeNe laser

Abstract

Theoretical considerations and experimental results related to the principle of dual-wavelength absolute distance interferometry (ADI) are presented. It is predicted that the required initial uncertainty of a length to be measured was related to the synthetic wavelength, its sta- bility, and the length to be measured. An absolute distance measure- ment approach employing a dual-longitudinal-mode He-Ne laser is pro- posed. In this approach, a heterodyne interferometer with two acousto- optic modulators (AOMs) is used to directly measure the fractional fringe at the synthetic wavelength formed by them. The common optical path configuration in the simplified interferometer eliminates the influences that air turbulence and mechanical vibration have on measurement. Fac- tors that influence measurement accuracy are analyzed theoretically and experimentally. Mode mixing is determined as the main influence on the accuracy of the approach, and the error caused by it can be compen- sated through data processing if the amount of mode mixing is fixed. Additionally, an experimental result is presented that obtains an accu- racy of 140 mm for 25 m. © 1999 Society of Photo-Optical Instrumentation Engi- neers. (S0091-3286(99)01102-2)