Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring

TLDR

Quartz‑enhanced photoacoustic spectroscopy is a sensitive gas‑detection technique that typically requires frequent calibration and suffers from long response times. This work introduces beat‑frequency QEPAS to enable ultra‑sensitive, calibration‑free trace‑gas detection and rapid spectral scanning. By demodulating the quartz tuning fork’s transient response at a non‑resonant frequency, the beat‑frequency signal simultaneously yields the fork’s resonance frequency, Q‑factor, and gas concentration, with three semiconductor lasers providing the excitation source. BF‑QEPAS eliminates the need for calibration, allows continuous monitoring, and achieves lower detection limits with shorter averaging times than conventional PAS and QEPAS while precisely determining electrical QTF parameters.

Abstract

Abstract Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a sensitive gas detection technique which requires frequent calibration and has a long response time. Here we report beat frequency (BF) QEPAS that can be used for ultra-sensitive calibration-free trace-gas detection and fast spectral scan applications. The resonance frequency and Q -factor of the quartz tuning fork (QTF) as well as the trace-gas concentration can be obtained simultaneously by detecting the beat frequency signal generated when the transient response signal of the QTF is demodulated at its non-resonance frequency. Hence, BF-QEPAS avoids a calibration process and permits continuous monitoring of a targeted trace gas. Three semiconductor lasers were selected as the excitation source to verify the performance of the BF-QEPAS technique. The BF-QEPAS method is capable of measuring lower trace-gas concentration levels with shorter averaging times as compared to conventional PAS and QEPAS techniques and determines the electrical QTF parameters precisely.