Photoacoustic methane gas analyser based on a 3.3-mm optical parametric oscillator

We demonstrate a bench-scale prototype of a photoacoustic (PA) methane gas analyser that takes advantage of an optical parametric oscillator (OPO) based on a fan-out MgO:PPLN structure and resonant differential PA detector. The OPO emits in a repetitively pulsed mode (~1750 Hz) at an idler wavelength of ~3.3 mm with an average power of ~40–50 mW. Using the prototype laser PA gas analyser, we experimentally demonstrate the feasibility of measuring the background methane concentration in air (~2–3 ppm of CH₄). The threshold sensitivity of the PA gas analyser (1s) is determined to be ~49 ppb of CH₄