Ultra-sensitive ppb-level methane detection based on NIR all-optical photoacoustic spectroscopy by using differential fiber-optic microphones with gold-chromium composite nanomembrane

High-sensitivity miniature dual-resonance photoacoustic sensor based on silicon cantilever beam for trace gas sensing

“…By the linear fitting method, the slope, intercept and linearity are obtained as 3.2 × 10 −4 , .66±, and 0.98, respectively. Therefore, the concentration of CH 4 in the air can be calculated to be 1.83±0.06 ppm, which is in the range from 1.76 ppm to 3.37 ppm found in previous literatures [17] , [50] , [58] , [59] , [60] .

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“… Technology Laser wavelength (nm) Cavity volume (cm 3 ) MDL @ IT (ppb) NNEA (W∙cm −1 ∙Hz 1/2 ) Ref. Differential PAS 3200 15.33 3600 @ 1 s not stated [4] CEPAS 1650.96 4.19 1230 @ 10 s not stated [13] All-optical PAS 1650.96 205 64 @ 30 s not stated [16] Differential PAS 1650.96 33.25 36.45 @ 1 s 4.42 × 10 −10 [50] MR-PAS 1653.7 222 200 @ 400 s 2.9 × 10 −9 [51] LWIR-PAS 7760 not state 7 @ 1 s 5 × 10 −9 [52] QEPAS 7707 not state 18 @ 0.1 s not state [53] Dual-resonance PAS 1650.96 2.26 355 @ 1 s 2.7 × 10 −9 [ This paper ] …”

All-optical light-induced thermoacoustic spectroscopy for remote and non-contact gas sensing

“…At atmospheric pressure, the MDL for H 2 S detection is 422 ppb, which is ~ 3 times better than that of the conventional electrical LITS sensor system. Since the QTF does not need to be in contact with the target gas, the AO-LITS can realize non-contact measurement and avoid the interference of gas flow noise on highly-sensitive optical detection [13] , [14] . The detection sensitivity can be further improved by decreasing the operating pressure in the QTF-based FPI module (to obtain a higher quality factor of the QTF) and/or increasing the effective optical pathlength [25] , [53] .…”

“…Quart tuning fork (QTF) as a resonant acoustic-electric transducer based on its piezoelectric property has been successfully applied in trace gas photoacoustic sensing since 2002, which is called quartz-enhanced photoacoustic spectroscopy (QEPAS) [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] . The QTF has the advantages of a high resonance frequency, a high quality factor, a small size and a low cost, which enable the QEPAS sensor to have the immunity to ambient acoustic noise and the capability to analyze ultra-small volume gas samples with respect to the conventional PAS sensor based on a photoacoustic cell and a microphone [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] . However, the QTF required to be immersed in the target gas in the QEPAS sensor, so that the QTF can be corroded.…”

Small-volume highly-sensitive all-optical gas sensor using non-resonant photoacoustic spectroscopy with dual silicon cantilever optical microphones

“…Though there is a significant resonant amplification in the resonant PAC due to the enhancement effect of a stable standing wave, this scheme still consumes several tens or even hundreds of milliliters of sample gas [26] , [27] . Furthermore, the acoustic signal could be simply affected by the resonant frequency drift in the practical environment [28] , [29] , which limits practical implementations of resonant PAS sensors. In the aspect of cantilever microphones, Fonsen et al applied cantilever microphone based on Michelson interferometer (MI) to gas detection [30] , [31] .…”