Sub-doppler trace-gas photoacoustic spectroscopy

TL;DR

This paper demonstrates sub-Doppler saturation spectroscopy in a cavity-enhanced photoacoustic sensor at low and high pressures, achieving high sensitivity and resolution for trace-gas detection using low-power mid-infrared radiation.

Contribution

It introduces a novel approach to perform sub-Doppler spectroscopy in a photoacoustic sensor at low pressure, expanding the technique's applicability to high-resolution trace-gas analysis.

Findings

Sub-Doppler spectroscopy performed at low pressure in a photoacoustic sensor.

Achieved 5 ppb sensitivity with only 35 μW laser power.

Compatible with both low and high-pressure gas sensing.

Abstract

Molecules are emerging as new benchmark for metrology and fundamental physics research, driving the demand for spectroscopic techniques combining high sensitivity and resolution. Photoacoustic spectroscopy has proven to combine high sensitivity with appealing features like compactness, wavelength-independent and background-free detection. To date, photoacoustic sensing has mostly been focused on high-pressure applied trace-gas analysis, while accessing the low-pressure regime has been considered not compatible with efficient acoustic wave propagation. However, sensing gas samples at low pressure is the key to get access to high-resolution spectroscopy. Here, we demonstrate that sub-Doppler saturation spectroscopy can be performed on low-pressure trace gases in a cavity-enhanced photoacoustic sensor with mW-level mid-infrared radiation. Moreover, we show that the same setup can be operated at higher pressure, enabling trace-gas detection with 5 parts-per-billion sensitivity with a laser power as low as 35 microwatts. This allows to extend the unique advantages of the photoacoustic technique to metrology and fundamental physics and provides the mid-infrared with a cost-effective, flexible tool combining high sensitivity and resolution.