Quartz-enhanced photo-acoustic spectroscopy (QEPAS) is one of the most robust and sensitive trace-gas detection techniques, which in the mid-IR range offers the advantage of high sensitivity, compactness and fast time-response. One of the main features of the photoacoustic techniques is that no optical detection is re-quired. Thus, the use of the QEPAS technique in THz range would allow to avoid the use of low-noise but expensive, bulky and cryogenic bolometers. The results obtained in the development of QEPAS sensors for trace gas detection of several chemical species, employing mid-IR and THz laser sources will be reviewed. Nor-malized noise equivalent absorption coefficients (NNEA) down to 10-10 cm-1W/Hz½ and part per trillion concentration detection ranges have been attained.
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