Quantum limits and robustness of nonlinear intracavity absorption spectroscopy

Abstract

We investigate the limits of intracavity absorption spectroscopy with nonlinear media. Using a common theoretical framework, we compare the detection of a trace gas within (i) an undriven cavity with gain near and above threshold; (ii) a driven cavity with gain kept just below threshold; and (iii) a cavity driven close to the saturation point of a saturable absorber. These phase-transition-based metrology methods are typically quantum limited by spontaneous emission, and we compare them to the empty-cavity shot-noise-limited case. Although the fundamental limits achievable with nonlinear media do not surpass the empty-cavity limits, we show that nonlinear methods are more robust against certain technical noise models. This recognition may have applications in spectrometer design for devices operating in nonideal field environments.