Photoacoustic spectroscopy of NO$_2$ using a mid-infrared pulsed optical parametric oscillator as light source

TL;DR

This paper demonstrates a photoacoustic sensor for NO2 detection using a mid-infrared pulsed optical parametric oscillator, achieving high sensitivity and real-time trace gas measurement capabilities.

Contribution

It introduces a novel PA sensor setup with a resonant MIR OPO light source for NO2 detection, showing improved sensitivity and real-time measurement potential.

Findings

Detection limit of 1.6 ppmV in single shot

Detection limit of 14 ppbV at 170 seconds

Good agreement with HITRAN database data

Abstract

A photoacoustic (PA) sensor for spectroscopic measurements of NO$_2$-N$_2$ at ambient pressure and temperature is demonstrated. The PA sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared (MIR) optical parametric oscillator (OPO). Spectroscopic measurements of NO$_2$-N$_2$ in the 3.25 $\mu$m to 3.55 $\mu$m wavelength region with a resolution bandwidth of 5 cm$^{-1}$ and with a single shot detection limit of 1.6 ppmV ($\mu$mol/mol) is demonstrated. The measurements were conducted with a constant flow rate of 300 ml/min, thus demonstrating the suitability of the gas sensor for real time trace gas measurements. The acquired spectra is compared with data from the Hitran database and good agreement is found. An Allan deviation analysis shows that the detection limit at optimum integration time for the PAS sensor is 14 ppbV (nmol/mol) at 170 seconds of integration time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 3.3$\times 10^{-7}$ W cm$^{-1}$ Hz$^{-1/2}$.