High-sensitivity photoacoustic gas detector by employing multi-pass cell and fiber-optic microphone

Abstract

A high-sensitivity photoacoustic (PA) spectroscopy (PAS) system is proposed for dual enhancement from both PA signal excitation and detection by employing a miniaturized Herriott cell and a fiber-optic microphone (FOM). The length of the optical absorption path of the PA cell is optimized to ∼374 mm with 17 reflections. The volume of the PA cell is only 622 µL. The FOM is a low-finesse fiber-optic Fabry-Pérot (FP) interferometer. The two reflectors of the FP cavity are formed by a fiber endface and a circular titanium diaphragm with a radius of 4.5 mm and a thickness of 3 µm. A fast demodulated white-light interferometer (WLI) is utilized to measure the absolute FP cavity length. The acoustic responsivity of the FOM reaches 126.6 nm/Pa. Several representative PA signals of trace acetylene (C2H2) are detected to evaluate the performance of the trace gas detector in the near-infrared region. Experimental results show that the minimum detectable pressure (MDP) of the FOM is 3.8 µPa/Hz1/2 at 110 Hz. The noise equivalent minimum detection concentration is measured to be 8.4 ppb with an integration time of 100 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 1.4×10−9 cm−1·W·Hz−1/2.

An all-Optical Photoacoustic Sensor for the Detection of Trace Gas

“…The latter are more sensitive, due to the enhanced displacement obtained at the free end. The photoacoustic signal in such systems is mainly amplified by means of mechanical resonances, sometimes coupled with optical amplification, as has been shown in the recent work by Zhang et al [ 21 ], with the use of Heriott cells.…”

Application of the Photoacoustic Approach in the Characterization of Nanostructured Materials

“…The sensitivity of the signal to several parameters provides the possibility of developing a PA configuration for imaging the heterogeneities in materials with high contrast. Moreover, a significant advantage of the approach is the possibility of performing in situ measurements [6].…”

Quartz tuning fork-based demodulation of an acoustic signal induced by photo-thermo-elastic energy conversion

“…Compared with these two types of sensors, optical gas sensors have a different principle of light absorption. Therefore, optical sensors have multiple advantages over electrochemical and semiconductor gas sensors, such as the feature of fast response, selective, sensitive and non-destructive sensing, high resistivity to electromagnetic noise, and intrinsically safe detection [ [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] ]. They are widely used in numerous fields of combustion diagnostics, atmospheric monitoring and life sciences [ [14] , [15] , [16] , [17] , [18] ].…”