Enhanced near-infrared QEPAS sensor for sub-ppm level H2S detection by means of a fiber amplified 1582Â nm DFB laser

A power-boosted quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor is developed for sub-ppm H2S 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 depth for H2S detection at 6320.6 cm−1. The linearity of the sensor response to the laser power and H2S concentration confirms that saturation does not occur. With ∼1.4 W optical excitation power and 67 s averaging time, a H2S 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 H2S QEPAS sensors. A side-by-side sensitivity comparison for different sensor systems is also reported.