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9 May 2012 NIR diode laser-based QEPAS for acetylene detection
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Quartz-enhanced photoacoustic spectroscopy with a near infrared distributed feedback diode laser at 1.53 μm is demonstrated for acetylene detection at atmospheric pressure and room temperature. The P(9) absorption line in the ν13 band of C2H2 is selected for light absorption and photoacoustic pressure wave excitation. A pair of resonant tubes with optimal dimensions is used in combination with a quartz tuning fork for photoacoustic signal enhancement. The wavelength of diode laser is modulated at half of the resonant frequency of tuning fork for second harmonic signal detection. The effect of residual amplitude modulation is theoretically analyzed and compared with the experimental results. A noise-limited minimum detectable concentration (1σ) of 2 part-per-million (ppm) is achieved with a 7-mW laser power and a 1-s lock-in time constant, corresponding to a normalized noise equivalent absorption coefficient of 5.4×10-8 cm-1 W/√Hz.
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Yingchun Cao, Wei Jin, and Hoi Lut Ho "NIR diode laser-based QEPAS for acetylene detection", Proc. SPIE 8439, Optical Sensing and Detection II, 843928 (9 May 2012);

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