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

Abstract

In this work, we report on a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for hydrogen sulfide (H₂S) detection, exploiting a liquid-nitrogen-cooled THz quantum cascade laser (QCL) operating in pulsed mode. The spectrophone was designed to accommodate a THz QCL beam and consisted of a custom quartz tuning fork with a large prong spacing, coupled with acoustic resonator tubes. The targeted rotational transition falls at 2.87 THz (95.626 cm^-1), with a line-strength of 5.53 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∙</mml:mo></mml:math> 10^-20 cm/mol. A THz QCL peak power of 150 mW was measured at a heat sink temperature of 81 K, pulse width of 1 μs and repetition rate of 15.8 kHz. A QEPAS record sensitivity for H₂S detection in the THz range of 360 part-per-billion in volume was achieved at a gas pressure of 60 Torr and 10 s integration time.