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 μm 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 (1σ) is determined to be ∼ 49 ppb of CH₄.

中文翻译：

---

基于 3.3-μm 光学参量振荡器的光声甲烷气体分析仪

我们展示了光声 (PA) 甲烷气体分析仪的工作台原型，该原型利用了基于扇出 MgO: PPLN 结构和谐振差分 PA 检测器的光学参量振荡器 (OPO)。OPO 以重复脉冲模式（~1750 Hz）以~3.3 μm 的闲散波长发射，平均功率为~40 – 50 mW。使用原型激光 PA 气体分析仪，我们通过实验证明了测量空气中背景甲烷浓度（~ 2 – 3 ppm 的 CH ₄）的可行性。PA 气体分析仪的阈值灵敏度 (1 σ ) 确定为 ~ 49 ppb 的 CH ₄。