Parts-per-billion detection of carbon monoxide: A comparison between quartz-enhanced photoacoustic and photothermal spectroscopy

Abstract

We report on a comparison between two optical detection techniques, one based on a Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) detection module, where a quartz tuning fork is acoustically coupled with a pair of millimeter-sized resonator tubes; and the other one based on a Photothermal Spectroscopy (PTS) module where a Fabry-Perot interferometer acts as transducer to probe refractive index variations. When resonant optical absorption of modulated light occurs in a gas sample, QEPAS directly detects acoustic waves while PTS probes refractive index variations caused by local heating. Compact QEPAS and PTS detection modules were realized and integrated in a gas sensor system for detection of carbon monoxide (CO), targeting the fundamental band at 4.6 μm by using a distributed-feedback quantum cascade laser. Performance was compared and ultimate detection limits up to ∼ 6 part-per-billion (ppb) and ∼15 ppb were reached for QEPAS and the PTS module, respectively, using 100 s integration time and 40 mW of laser power.

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.…”

Compact and portable quartz-enhanced photoacoustic spectroscopy sensor for carbon monoxide environmental monitoring in urban areas

“…Since the laser is modulated, pressure waves, i.e., sound waves, are generated, further detected employing a quartz tuning fork (QTF) as a sound-to-current transducers, due to the quartz piezoelectric properties [9] , [10] , [11] . QEPAS, along with other QTF-based techniques, has been already demonstrated to be capable to perform CO real time detection in the sub-ppm range [8] , [12] , [13] , [14] , [15] or even in the ppt range [16] . However, CO is a slow relaxer for the typical QTF operating frequencies ( ) and the QEPAS signal is strongly affected by the presence of relaxation promoters in the mixture.…”

Sensitivity enhanced NIR photoacoustic CO detection with SF6 promoting vibrational to translational relaxation process

“…Carbon monoxide (CO) is a colorless, odorless and highly toxic gas, which is emitted from the incomplete combustion of fossil fuels, organic compounds. Evidences show that excessive exposure to CO can cause dizziness, confusion, unconsciousness and even death [1] . A safe exposure limitation of 9 ppm CO concentration for an 8-h period has been adopted by the US Environmental Protection Agency (EPA) [2] .…”