All-optical QEPAS trace gas senor employing an optical amplification technique
Quartz-Enhanced Photoacoustic Spectroscopy(QEPA)technology has become a kind of trace gas detection technology due to its advantages of high sensitivity,strong immunity to noise and compact size.An all-optical QEPA trace gas detection system was designed.A quartz tuning fork with a resonant frequency of 32.7 kHz was employed as the acoustic sen-sor,and the system signal amplitude was greatly enhanced by employing an optical power amplification technology.A fiber-op-tic Fabry-Perot interferometer with self-stabilizing characteristics was used as the vibration demodulation unit,significantly im-proving system stability.Acetylene(C2H2)was selected as the target gas for detection.A tunable semiconductor laser with a output wavelength of 1.5 μm was used as the excitation light source.By combining wavelength modulation and second harmon-ic demodulation techniques,the optimal modulation depth was determined to be 0.171 cm-1,and the optimal distance between the laser position and the bottom of the tuning fork was found to be 0.8 mm.The QEPAS signal exhibited linear variation with C2 H2 concentration,with a linearity of 0.998.The system detection limit was 30.3 ppb,corresponding to a normalized equiva-lent noise coefficient of 2.51×10-8 cm-1·W·Hz-1/2.Finally,under the same conditions,a continuous working test for one hour was conducted,verifying the excellent stability of the system.
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