Abstract
A highly sensitive photoacoustic (PA) gas sensor using a miniaturized Herriott-type multi-pass cell is reported. A cylindrical concave mirror and a cylindrical planar mirror are utilized as the two reflectors of the Herriott cell. The total length of optical path is optimized to be 0.609 m with 29 reflections. To eliminate the effect of the cell wall absorption, we employ the second-harmonic (2f) wavelength modulation spectroscopy (2f-WMS) method. Trace acetylene (C2H2) was introduced into the PA cell to investigate the performance of the sensor. Experimental results show that this gas sensor has an excellent linear characteristic and a long-term stability. Allan-Werle deviation analysis results show that the minimum detection concentration (MDC) is calculated as 12.2 ppb with a 400-s average time. Moreover, a normalized noise-equivalent absorption (NNEA) coefficient was achieved to be 3.3 × 10−9 Wcm-1 Hz-1/2.
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