Cavity-enhanced absorption sensing with robust sideband locking

TL;DR

This paper introduces a robust, high-bandwidth cavity-enhanced absorption sensing method using PDH sideband locking, achieving high sensitivity and compatibility with weak probe beams for precise optical absorption measurements.

Contribution

The authors develop a simple, continuous cavity-enhanced absorption measurement technique based on PDH sideband locking, demonstrating its effectiveness with a proof-of-concept cavity.

Findings

Achieved absorption sensitivity of 6.6 x 10^{-11} cm^{-1}/√Hz at 100 kHz

Demonstrated sensitivity of ~10^{-10} cm^{-1}/√Hz from 30 kHz to 1 MHz

Collected 38 μW from the cavity's circulating power

Abstract

We present a simple, continuous, cavity-enhanced optical absorption measurement technique based on high-bandwidth Pound-Drever-Hall (PDH) sideband locking. The technique provides a resonant amplitude quadrature readout that can be mapped onto the cavity's internal loss rate, and is naturally compatible with weak probe beams. With a proof-of-concept 5-cm-long Fabry-Perot cavity, we measure an absorption sensitivity of $6.6 \times 10^{-11} ~\text{cm}^{-1}/\sqrt{\text{Hz}}$ at 100 kHz (roughly the cavity bandwidth) and $\sim 10^{-10}~\text{cm}^{-1}/\sqrt{\text{Hz}}$ from 30 kHz to 1 MHz, with $38~\mu$W collected from the cavity's circulating power.