Modified laser scanning technique in wavelength modulation spectroscopy for advanced TDLAS gas sensing

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

“…Optical methods using laser absorption spectroscopy (LAS) based on the ‘finger-print’ absorption lines of molecules, such as tunable diode laser absorption spectroscopy (TDLAS), cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS) [7] , [8] , [9] , [10] , have been widely investigated for trace gas detection. TDLAS-based sensors have been widely commercialized [11] , and it fundamentally relies on the long optical path and superior photodetectors to achieve favorable sensing performance. Also, ultra-stable cavity mode is essential in CRDS, which limits practical implementations.…”

Application and algorithm research of TDLAS

“…After introducing the nonlinear half-wave scanning, the corresponding scanning function was designed to expand the strong absorption around the time window, thereby deriving other considerable waveform data. Under finite sampling rate in TDLAS signal procession, nonlinear half-wave scanning was used, and the second harmonic fluctuation was only 1/3 of the traditional WMS-2f linear scanning [39]. Ang Huang et al introduced a back propagation (BP) neural network into a field programmable gate array (FPGA) chip to achieve faster response and higher signal-to-noise ratio (SNR) of TDLAS tomography in temperature and humidity imaging.…”

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

“…Though gas chromatography-mass spectrometry has high sensitivity to detect volatile and semi-volatile organic compounds, its columns need to be maintained regularly and are always with time consumption [8] . The optical gas sensing technology, such as tunable diode laser absorption spectroscopy (TDLAS) [9] , [10] and photoacoustic spectroscopy (PAS) [11] , [12] , [13] , has been widely applied because of their fast response, high sensitivity and selectivity. The gas detection based on TDLAS is achieved by detecting the attenuation of optical power, and the detection sensitivity is proportional to the gas absorption optical length.…”