A quartz enhanced photoacoustic spectroscopy (QEPAS) sensor, employing an erbium-doped fiber amplified laser source and a custom quartz tuning fork (QTF) with its two prongs spaced $800 lm apart, is reported. The sensor employs an acoustic micro-resonator (AmR) which is assembled in an "on-beam" QEPAS configuration. Both length and vertical position of the AmR are optimized in terms of signal-to-noise ratio, significantly improving the QEPAS detection sensitivity by a factor of $40, compared to the case of a sensor using a bare custom QTF. The fiber-amplifier-enhanced QEPAS sensor is applied to H 2 S trace gas detection, reaching a sensitivity of $890 ppb at 1 s integration time, similar to those obtained with a power-enhanced QEPAS sensor equipped with a standard QTF, but with the advantages of easy optical alignment, simple installation, and long-term stability.

A sub-ppb level photoacoustic spectroscopy (PAS)-based sensor for nitrogen dioxide (NO 2) detection was developed by means of a 3.5 W CW multimode diode laser emitting at 447 nm. A differential photoacoustic cell was designed to match the imperfect laser beam and reduce the external acoustic as well as the electromagnetic noise. The diode laser power, gas flow and pressure of the sensor were optimized, which resulted in a NO 2 sensor system with a detection limit of 54 pptv with a 1-s averaging time and an excellent linear dynamic range over > three orders of magnitude. The impact of water vapor as the catalyst on the photoacoustic signal amplitude was also investigated. Continuous measurements covering an eight-day period were performed to demonstrate the stability and robustness of the reported PAS-based NO 2 sensor system.

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Enhanced near-infrared QEPAS sensor for sub-ppm level H 2 S detection by means of a fiber amplified 1582nm DFB laser, Sensors and Actuators B: Chemical (2015), http://dx. Abstract:A power-boosted quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor is developed for sub-ppm H 2 S trace-gas detection in the near-infrared spectral region. The sensor is based on off-beam QEPAS with an erbium-doped fiber amplified 1582 nm distributed feedback (DFB) laser. The offset of the sensor floor noise caused by stray light and gas flow can be removed by an electrical modulation cancellation method, which lowers the noise to the theoretical thermal noise level. The sensor was optimized in terms of gas pressure and current modulation A c c e p t e d M a n u s c r i p 2 depth for H 2 S detection at 6320.6 cm -1 . The linearity of the sensor response to the laser power and H 2 S concentration confirms that saturation does not occur. With ~ 1.4 W optical excitation power and 67 sec averaging time, a H 2 S detection sensitivity of 142 ppbv (parts per billion by volume) is achieved at atmospheric pressure and room temperature, which is the best value, reported in the literature so far for H 2 S QEPAS sensors. A side-by-side sensitivity comparison for different sensor systems is also reported.

Quartz-enhanced photoacoustic spectroscopy (QEPAS) with a single-tube acoustic microresonator (AmR) inserted between the prongs of a custom quartz tuning fork (QTF) was developed, investigated, and optimized experimentally. Due to the high acoustic coupling efficiency between the AmR and the QTF, the single-tube on-beam QEPAS spectrophone configuration improves the detection sensitivity by 2 orders of magnitude compared to a bare QTF. This approach significantly reduces the spectrophone size with respect to the traditional on-beam spectrophone configuration, thereby facilitating the laser beam alignment. A 1σ normalized noise equivalent absorption coefficient of 1.21×10(-8) cm(-1)·W/√Hz was obtained for dry CO2 detection at normal atmospheric pressure.