Sensitive multi-species photoacoustic gas detection based on mid-infrared supercontinuum source and miniature multipass cell

TL;DR

This paper introduces a sensitive, broadband photoacoustic gas detection system using a mid-infrared supercontinuum source and a miniature multipass cell, achieving high sensitivity and selectivity for multiple trace gases.

Contribution

It presents a novel FT-PAS system with a supercontinuum source and a miniature Herriott cell, significantly improving detection limits and enabling multi-species detection in small samples.

Findings

Achieved 11 ppb detection limit for methane.

Improved sensitivity by a factor of 12 over previous FT-PAS systems.

Demonstrated reliable multi-species identification in complex gas mixtures.

Abstract

We report multipass broadband photoacoustic spectroscopy of trace gases in the mid-infrared. The measurement principle of the sensor relies on supercontinuum-based Fourier transform photoacoustic spectroscopy (FT-PAS), in which a scanning interferometer modulates the intensity of a mid-infrared supercontinuum light source and a cantilever microphone is employed for sensitive photoacoustic detection. With a custom-built external Herriott cell, the supercontinuum beam propagates ten times through a miniature and acoustically non-resonant gas cell. The performance of the FT-PAS system is demonstrated by measuring the fundamental C-H stretch bands of various hydrocarbons. A noise equivalent detection limit of 11 ppb is obtained for methane (40 s averaging time, 15 $\mu$W/cm$^{-1}$ incident power spectral density, 4 cm$^{-1}$ resolution), which is an improvement by a factor of 12 compared to the best previous FT-PAS systems. High linearity and good stability of the sensor provide reliable identification of individual species from a gas mixture with strong spectral overlap, laying the foundation for sensitive and selective multi-species detection in small sample volumes.