Ammonia sensor based on QEPAS with HC-PBF as reference cell

Abstract

Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors involves with many desirable features, such as being small and portable, with fast continuous in situ measurements possible. In QEPAS systems, reference cells filled with gas mixtures for wavelength locking and calibration are used to improve the precision and stability of the trace gas concentration measurement. For this study, a 5 m length hollow core photonic bandgap fiber (HC-PBF) splicing with single mode fibers at two ends was manufactured as reference cell, which has long absorption path, low transmission loss and easy connectivity. Hollow cores under high pressure (3.0× 10 5 Pa) were filled with a certified mixture of ammonia and nitrogen gas to reach equilibrium rapidly. The experiment results indicated that absorption spectra of reference cell with a low loss <3.5dB maintained stable after 150 days at atmosphere. For trace gas detection, 1.531 μm DFB laser with wavelength modulation technique was demonstrated based on QEPAS. A normalized noise equivalent absorption coefficient (NNEA) of 1.18×10 -7 cm -1 W/√Hz was obtained at room temperature and pressure of 760 Torr. This results in a minimum detection limit of 3.6ppm for noise equivalent concentration within a 1s lock in integration time.

High-Power DFB Diode Laser-Based CO-QEPAS Sensor: Optimization and Performance

“…The QEPAS sensor performance can be significantly improved when an acoustic micro-resonator (MR) is added. There are two main kinds of micro-resonators, an on-beam and an off-beam MR [ 30 , 31 , 32 ]. Compared to an off-beam configuration, the on-beam has the advantage of a stronger acoustic coupling efficiency.…”

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

“…The high Q-factor (~100,000 in a vacuum and~10,000 in a standard atmosphere pressure) and narrow resonance frequency band (<1 Hz) of QTF improve the QEPAS selectivity and immunity to environmental acoustic noise [13][14][15][16][17][18][19]. Due to the merits of high selectivity and sensitivity, low cost, compactness, and a large dynamic range, QEPAS sensors have been widely applied in gas detection for atmospheric monitoring [20][21][22][23][24][25][26][27], chemical analysis [28][29][30][31][32], biomedical diagnostics [33][34][35][36], and trace gas sensing [37][38][39][40][41][42][43][44]. Different QEPAS sensor architectures were developed to meet the requirements of a large number of applications.…”