Compact quantum cascade laser based quartz-enhanced photoacoustic spectroscopy sensor system for detection of carbon disulfide

Abstract

A compact gas sensor system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) employing a continuous wave (CW) distributed feedback quantum cascade laser (DFB-QCL) operating at 4.59 µm was developed for detection of carbon disulfide (CS₂) in air at trace concentration. The influence of water vapor on monitored QEPAS signal was investigated to enable compensation of this dependence by independent moisture sensing. A 1 σ limit of detection of 28 parts per billion by volume (ppbv) for a 1 s lock-in amplifier time constant was obtained for the CS₂ line centered at 2178.69 cm^-1 when the gas sample was moisturized with 2.3 vol% H₂O. The work reports the suitability of the system for monitoring CS₂ with high selectivity and sensitivity, as well as low sample gas volume requirements and fast sensor response for applications such as workplace air and process monitoring at industry.

Laser spectroscopy for breath analysis: towards clinical implementation

“…Special features are: (a) ambient acoustic noise is low at those frequencies; (b) external sound will not excite the piezoelectrically active mode of the prongs; (c) the width of resonance is 4 Hz (at atmospheric pressure) and only frequency components in this narrow spectral band can produce efficient excitation of the TF vibration; and (d) the gas sampling volume is extremely small (0.15 mm 3 ) [72]. There are a number of examples of breath studies using QEPAS, such as: (i) determining the 13 CO 2 /CO 2 ratio from human breath for identification of Helicobacter pylori infection, liver malfunction, and excessive growth of bacteria in the body [73]; (ii) the detection of carbon disulfide (CS 2 ) to indicate cirrhosis and a potential non-invasive marker of respiratory bacterial colonization in cystic fibrosis [74]; and (iii) NH 3 detection as product of protein metabolism relevant for a number of disease states and human physiology [75].…”

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.…”

Mid-infrared sensing of CO at saturated absorption conditions using intracavity quartz-enhanced photoacoustic spectroscopy

“…The detector signal shown in Fig. 2 also served for locking the laser center wavelength to a cavity resonance based on a standard wavelength modulation approach [37]. To this end, the signal was demodulated at the first harmonic of the modulation frequency using the lock-in amplifier.…”

“…For measurements of CO, a reference gas cell containing CO was used to lock the laser wavelength to the CO resonance. The third harmonic of the signal from the photo-detector recording the transmission through the reference cell was used for this purpose [37].…”