H2S quartz-enhanced photoacoustic spectroscopy sensor employing a liquid-nitrogen-cooled THz quantum cascade laser operating in pulsed mode

Integrated near-infrared QEPAS sensor based on a 28 kHz quartz tuning fork for online monitoring of CO2 in the greenhouse

“…The novelty of this technology lies in the use of industrial mass-produced quartz tuning fork (QTF) as the acoustic wave transducer, replacing the miniature microphone in the traditional PAS, and realizing highly sensitive detection of weak photoacoustic signals [20] , [21] , [22] . QEPAS has become a research hotspot in recent years due to its immunity to environmental noise, high detection sensitivity, small size, wide dynamic range, and QTF operation insensitive to the excitation wavelength [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] . In recent years, researchers have used QEPAS technology to detect and analyze CO 2 gas concentration.…”

Independent Control of Mode Selection and Power Extraction in Terahertz Semiconductor Lasers

“…It is interesting to point out that these THz-ADBR-GC-QCL devices have been utilized to detect H 2 S gas track by means of photoacoustic spectroscopy, and a detection limit down to 360 ppb has been realized. 39…”

Ppb-level gas detection using on-beam quartz-enhanced photoacoustic spectroscopy based on a 28 kHz tuning fork

“…To obtain higher QEPAS signals, custom QTFs with lower resonance frequencies were developed for QEPAS system since 2014 by Spagnolo et al [10] , [11] , [12] , [13] , [14] . The availability of custom QTFs with a large prong spacing opened the way to the employment of high-power fiber-amplified near-IR lasers and THz lasers in QEPAS system [15] , [16] , [17] , [26] , thanks to the reduction of the photothermal background noise caused by portion of the laser beam hitting the QTF, due to the poor beam quality of these laser sources. Several other breakthroughs in QEPAS development have been demonstrated using custom QTFs.…”