Quantitative test of general theories of the intrinsic laser linewidth

TL;DR

This paper performs first-principles numerical calculations of the quantum-limited laser linewidth, validating recent theoretical predictions against traditional models through detailed simulations of the Maxwell-Bloch equations with noise.

Contribution

It provides the first numerical validation of the noisy steady-state ab initio laser theory (N-SALT) predictions for laser linewidths, including effects of dispersion, losses, and non-linear coupling.

Findings

Quantitative agreement between N-SALT and simulations on linewidth variation.

Validation of side-peak emergence due to relaxation oscillations.

Inclusion of dispersion, losses, and non-linear effects in linewidth predictions.

Abstract

We perform a first-principles calculation of the quantum-limited laser linewidth, testing the predictions of recently developed theories of the laser linewidth based on fluctuations about the known steady-state laser solutions against traditional forms of the Schawlow-Townes linewidth. The numerical study is based on finite-difference time-domain simulations of the semiclassical Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus includes the effects of dispersion, losses due to the open boundary of the laser cavity, and non-linear coupling between the amplitude and phase fluctuations ($\alpha$ factor). We find quantitative agreement between the numerical results and the predictions of the noisy steady-state ab initio laser theory (N-SALT), both in the variation of the linewidth with output power, as well as the emergence of side-peaks due to relaxation oscillations.