A low cost scheme for high precision dual-wavelength laser metrology

TL;DR

This paper presents a cost-effective dual-wavelength laser metrology method using direct fringe detection and simple control systems, achieving nanometer precision suitable for astrometric interferometry without complex stabilization.

Contribution

The work introduces a novel, low-cost dual-wavelength metrology technique that does not require frequency-stabilized lasers and minimizes additional optical components.

Findings

Achieves nanometer precision in optical path measurement.

Uses simple, inexpensive components and direct fringe detection.

Applicable to high-precision astrometric interferometry.

Abstract

A novel method capable of delivering relative optical path length metrology with nanometer precision is demonstrated. Unlike conventional dual-wavelength metrology which employs heterodyne detection, the method developed in this work utilizes direct detection of interference fringes of two He-Ne lasers as well as a less precise stepper motor open-loop position control system to perform its measurement. Although the method may be applicable to a variety of circumstances, the specific application where this metrology is essential is in an astrometric optical long baseline stellar interferometer dedicated to precise measurement of stellar positions. In our example application of this metrology to a narrow-angle astrometric interferometer, measurement of nanometer precision could be achieved without frequency-stabilized lasers although the use of such lasers would extend the range of optical path length the metrology can accurately measure. Implementation of the method requires very little additional optics or electronics, thus minimizing cost and effort of implementation. Furthermore, the optical path traversed by the metrology lasers is identical with that of the starlight or science beams, even down to using the same photodetectors, thereby minimizing the non-common-path between metrology and science channels.