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We proposed a new method for gas detection in photoacoustic spectroscopy based on acousto-optic Q-switched fiber laser by merging a transmission PAS cell (resonant frequency f 0 = 5.3 kHz) inside the fiber laser cavity. The Q-switching was achieved by an acousto-optic modulator, achieving a peak pulse power of ~679 mW in the case of the acousto-optic modulation signal with an optimized duty ratio of 10%. We used a custom-made fiber Bragg grating with a central wavelength of 1530.37 nm (the absorption peak of C2H2) to select the laser wavelength. The system achieved a linear response (R2 = 0.9941) in a concentration range from 400 to 7000 ppmv, and the minimum detection limit compared to that of a conventional intensity modulation system was enhanced by 94.2 times. [ABSTRACT FROM AUTHOR]

• A long-path QEPTS gas sensor using a high power Q-switched fiber laser was proposed. • Long optical path and high power are beneficial to the QEPTS sensor. • A minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time was achieved. A long-path quartz tuning fork enhanced photothermal spectroscopy (QEPTS) gas sensor using a Q-switched fiber laser is proposed. A theoretical model is used to describe the process of the long-path QEPTS sensor and the factors that affect its performance. We can conclude that long optical path and high power are beneficial to the QEPTS sensor from the theoretical analysis. And we use our long-path QEPTS sensor for C 2 H 2 detection at the wavelength of 1531.59 nm. With the scanning time of 4 s and the peak pulse power of 127.5 mW, an Allan deviation analysis shows that our sensor has a minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time and a good linear response (R-square = 0.99796). [ABSTRACT FROM AUTHOR]

In this paper, we reported a new multi-point sensor for C 2 H 2 detection based on photoacoustic spectroscopy and acousto-optic Q-switched fiber laser. Three transmission-type PAS cells were placed inside the fiber laser cavity and used for C 2 H 2 detection simultaneously to demonstrate the potential of spatially resolved measurements. A maximum pulse peak power of ∼544 mW was generated by the acousto-optic Q-switched fiber laser. The signal-to-noise ratios (SNR) calculated from the experimental results was 57.7 dB, 45.1 dB and 57.2 dB. This resulted in a minimum detection limit (MDL) for C 2 H 2 of 1.73 ppmv, 7.82 ppmv and 1.93 ppmv for PAS cell 1, PAS cell 2 and PAS cell 3, respectively. [ABSTRACT FROM AUTHOR]

• A scanned-wavelength intra-cavity QEPAS sensor with injection seeding technique and Q-switched technique was reported. • The Q-switched fiber laser has a peak pulse power of 0.88 W. • A minimum detection limit (MDL) of 507 ppbv was achieved. A high sensitivity scanned-wavelength intra-cavity quartz enhanced photoacoustic spectroscopy (QEPAS) system, based on injection seeding technique and Q-switched technique, was proposed in this paper. In this system, the gas cell was placed in the acousto-optic Q-switched fiber laser cavity, and the high power Q-switched pulses were used to acoustic wave excitation. A distributed feedback (DFB) diode laser with a wavelength scanning range from 1532.63 nm to 1533.03 nm was used as the seed laser to select the laser wavelength. The laser power emitted by the seed laser operating at an injection current of 56 mA (the gas absorption peak) was 3 mW. A custom-made broadband fiber Bragg grating (FBG) with a bandwidth of 500 pm (picometer) was used to stabilize the cavity operation and suppress the amplified spontaneous emission (ASE) spectrum. With an intra-cavity peak pulse power of 0.88 W, the system achieved a minimum detection limit (MDL) of 507 ppbv at atmospheric pressure and room temperature, corresponding to a normalized noise-equivalent absorption (NNEA) of 1.616 × 10−8 W cm−1 Hz−1/2. [ABSTRACT FROM AUTHOR]