Optical frequency comb spectroscopy at 3-5.4 {\mu}m with a doubly resonant optical parametric oscillator

TL;DR

This paper introduces a versatile mid-infrared frequency comb spectroscopy system using a doubly resonant optical parametric oscillator, enabling high-precision broadband absorption measurements and continuous-filtering Vernier spectroscopy in the 3-5.4 μm range.

Contribution

It demonstrates a novel mid-infrared frequency comb spectroscopy system with dual detection methods and first-time application of continuous-filtering Vernier spectroscopy in this spectral region.

Findings

High-precision broadband absorption spectra of methane, nitric oxide, and atmospheric gases.

Detection limits of 10-20 ppb Hz$^{-1/2}$ for key gases.

First implementation of continuous-filtering Vernier spectroscopy in the mid-infrared.

Abstract

We present a versatile mid-infrared frequency comb spectroscopy system based on a doubly resonant optical parametric oscillator tunable in the 3-5.4 {\mu}m range and two detection methods, a Fourier transform spectrometer (FTS) and a Vernier spectrometer. Using the FTS with a multipass cell we measure high-precision broadband absorption spectra of CH$_4$ and NO at ~3.3 {\mu}m and ~5.2 {\mu}m, respectively, and of atmospheric species (CH$_4$, CO, CO$_2$ and H$_2$O) in air in the signal and idler wavelength range. The figure of merit of the system is on the order of 10$^{-8}$ cm$^{-1}$ Hz$^{-1/2}$ per spectral element, and multiline fitting yields minimum detectable concentrations of 10-20 ppb Hz$^{-1/2}$ for CH$_4$, NO and CO. For the first time in the mid-infrared, we perform continuous-filtering Vernier spectroscopy using a low finesse enhancement cavity, a grating and a single detector, and measure the absorption spectrum of CH$_4$ and H$_2$O in ambient air at ~3.3 {\mu}m.