Cavity-immune features in the spectra of superradiant crossover laser pulses

TL;DR

This paper explores how cavity-immune spectral features emerge in superradiant crossover laser pulses operating in a regime where Doppler broadening exceeds cavity linewidth, revealing noise reduction mechanisms via cavity detuning.

Contribution

It demonstrates cavity noise immunity in pulsed superradiant lasers through cavity detuning, supported by experimental data and a Tavis-Cummings model analysis.

Findings

Cavity detuning reduces cavity noise influence on lasing frequency.

Velocity-dependent dynamics contribute to noise immunity.

Experimental results align with the theoretical model.

Abstract

Lasing in the bad cavity regime has promising applications in precision metrology due to the reduced sensitivity to cavity noise. Here we investigate the spectral properties and phase behavior of pulsed lasing on the $^1$S$_0 - ^3$P$_1$ line of $^{88}$Sr in a mK thermal ensemble, as first described in arxiv:1903.12593. The system operates in a regime where the Doppler-broadened atomic transition linewidth is several times larger than the cavity linewidth. We find that by detuning the cavity resonance, the influence of the cavity noise on the peak lasing frequency can be eliminated to first order despite the system not being deep in the bad cavity regime. Experimental results are compared to a model based on a Tavis-Cummings Hamiltonian, which enables us to investigate the interplay between different thermal velocity classes as the underlying mechanism for the reduction in cavity noise. These velocity-dependent dynamics can occur in pulsed lasing and during the turn-on behavior of lasers in the superradiant crossover regime.