Pulsed Frequency Shifted Feedback Laser for Accurate Long Distance Measurements: Beat Order Determination

TL;DR

This paper demonstrates that pulsed Frequency Shifted Feedback laser interferometry can achieve accurate long-distance measurements up to 240 meters by real-time beat order determination, emphasizing the importance of stabilizing the acoustic frequency.

Contribution

It introduces a simple real-time method for beat order determination in long-distance FSF laser interferometry, validated up to 240 meters, and discusses models explaining the measurement accuracy.

Findings

Measurement accuracy depends on stabilizing the acoustic frequency.

The moving-comb model does not fit the experimental results.

Real-time beat order determination enables high-precision measurements.

Abstract

Long-distance measurements (10 m - 1000 m) with an accuracy of 10-7 is a challenge for many applications. We show that it is achievable with Frequency Shifted Feedback (FSF) laser interferometry technique, provided that the determination of the radio frequency beat order be made without ambiguity and on a time scale compatible with atmospheric applications. Using the pulsed-FSF laser that we developed for laser guide star application, we propose and test, up to 240 m, a simple method for measuring the beat order in real time. The moving-comb and Yatsenko models are also discussed. The first of these models fails to interpret our long-distance interferometry results. We show that the accuracy of long-distance measurements depends primarily on the stabilization of the acoustic frequency of the modulator.