Control of the differential interference contrast in reinjected bimode laser

TL;DR

This paper demonstrates how to control the interference contrast in a bimode laser using frequency shifts, enabling enhancement or cancellation of interference patterns in laser imaging.

Contribution

It introduces a method to control interference contrast in bimode lasers through frequency shift adjustments, both theoretically and experimentally.

Findings

Interference contrast of total laser intensity is always maximal and independent of frequency shift.

Contrast of individual polarization states depends on frequency, peaking at resonance frequencies.

Contrast can be canceled at intermediate frequencies between resonance peaks.

Abstract

We have demonstrated, both theoretically and experimentally, that it is possible to control (i.e., to enhance or cancel) the contrast of the interference pattern appearing in the intensity images obtained with a laser optical feedback imaging (LOFI) setup using a bimode laser. The laser is composed of two coupled orthogonally polarized states that interact (i.e., interfere) through the cross saturation laser dynamics. We created the contrast control by choosing the frequency shift (i.e., the beating frequency) between the feedback electric fields and the intracavity electric fields. We have shown that the interference contrast of the output power modulation of the laser total intensity is independent from the frequency shift and is always maximal. On the other hand, the interference contrast of each polarization state is frequency dependent. We obtained the maximal contrast when the frequency shift was equal to one of the resonance frequencies of the bimode dynamics, and was very low (and almost cancels) for an intermediate frequency located at the intersection of the two resonance curves.