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An intra‐cavity quartz‐enhanced photoacoustic spectroscopy (QEPAS) sensor using fiber‐ring laser is demonstrated. The sensor includes an erbium‐doped fiber (EDF) intra‐cavity laser and a quartz tuning fork (QTF), and realizes wavelength scanning through a piezoelectric transducer (PZT). The acousto‐optic modulator (AOM) is used to modulate laser intensity at a frequency of 32.758 kHz. We use optical switches to detect acetylene (C2H2) and carbon dioxide (CO2) at 1530.37 and 1572.66 nm, respectively, based on the time division multiplexing (TDM) technology. The two‐component gas sensor showed good linearity of 0.9996 and 0.9966, and could achieve a minimum detection limit (MDL) of 180.64 ppbv and 145.45 ppmv for C2H2 and CO2 detection, respectively. [ABSTRACT FROM AUTHOR]

A compact and low-power-consumption gas sensor using a quantum cascade laser (QCL) emitting at 4.6 μm for measurement of carbon monoxide (CO) was proposed and experimentally demonstrated. A compact sensor structure with a physical dimension of 14 × 10 × 6.5 cm3 was designed. A new intermittent scanning technique was used to drive the QCL to reduce the power consumption of the system. In this technique, the power consumption of the sensor is as low as 1.08 W, which is about 75% lower than the conventional direct absorption technology. The stability of the CO sensor was demonstrated by continuously monitoring CO concentration for more than 1 h. In the concentration range of 10 ppm to 500 ppm, the CO sensor exhibited a satisfactory linear response (R-square = 0.9998). With an integration time of 202 s, the minimum detection limit was increased to 4.85 ppb, based on an Allan deviation analysis. [ABSTRACT FROM AUTHOR]

• The baseline signal is corrected and the absorbance signal is denoised by using the fitting neural network. • Based on a simple system structure, it is possible to increase the SNR of the absorbance signal to about 20 dB. • Line shape function is used for feature selection to reduce the training difficulty of the neural network. We designed a methane/ethane (CH 4 /C 2 H 6) dual-gas sensor on the basis of direct absorption spectroscopy (DAS) technology and explored the potential for low power consumption and miniaturization of the detection system using the effective optical range is only 25 cm for absorption cell and an uncooled photodetector. The problem of baseline drift introduced by uncooled photodetectors has been improved by using of a fitting neural network approach, and absorbance spectrum denoising has been realized. We established the mathematical relationship between absorbance and concentration for each gas of CH 4 /C 2 H 6 through experimental detection, which shows strong linearity. And the correlation coefficients (R2) reached 0.99995 and 0.99998, demonstrating the robustness of the sensor. Through 3 h of measured and evaluated system, we obtained the minimum detectable column densities of 0.588 ppm⋅m and 0.128 ppm⋅m for CH 4 and C 2 H 6 , respectively, which proved that the sensor has high sensitivity, strong stability, and has broad application prospects. [ABSTRACT FROM AUTHOR]

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]

• In this paper, a two-component gas sensing system in the resonant cavity of the fiber ring laser based on photoacoustic spectroscopy (PAS) is designed by embedding the PAS cell into the laser resonant cavity. • A ring cavity erbium-doped fiber (EDF) laser is built in this system, combined with a longitudinal resonant PAS cell to detect the PAS signal, and a custom-designed wavelength modulator uses the fiber bragg grating (FBG) to paste the piezoelectric transducer (PZT) for scanning and modulating the gas absorption wavelength. • The gas concentration is calculated by the second harmonic (2f) PAS signal. Based on time division multiplexing (TDM) technology, the acetylene (C 2 H 2) and carbon dioxide (CO 2) is detected respectively by the time-sharing operation of C-band and L-band EDFs for different wavelengths output. • The system can improve the laser power and eliminate the mode competition between the two output laser bands. • The two-component gas sensing system also showed superior gas sensing capability for trace gas detection and could achieve a minimum detection limit of 728 ppb and 503 ppm for C 2 H 2 and CO 2 detection, respectively. In this paper, a two-component gas sensing system in the resonant cavity of the fiber ring laser based on photoacoustic spectroscopy (PAS) is designed by embedding the PAS cell into the laser resonant cavity. A ring cavity erbium-doped fiber (EDF) laser is built in this system, combined with a longitudinal resonant PAS cell to detect the PAS signal, and a custom-designed wavelength modulator uses the fiber bragg grating (FBG) to paste the piezoelectric transducer (PZT) for scanning and modulating the gas absorption wavelength. The gas concentration is calculated by the second harmonic (2f) PAS signal. Based on time division multiplexing (TDM) technology, the acetylene (C 2 H 2) and carbon dioxide (CO 2) is detected respectively by the time-sharing operation of C-band and L-band EDFs for different wavelengths output. The time-sharing operation of the two wavelength laser is realized through optical switches, which effectively avoids the laser power loss and the instability of each wavelength caused by the mode competition phenomenon of multiple wavelengths. The detection performance of C 2 H 2 and CO 2 is implemented under normal temperature and pressure. The PAS signal intensity is further improved by optimizing the wavelength modulation amplitude and incident laser power. The linear fit (R2) and minimum detection limit (MDL) of C 2 H 2 and CO 2 are 0.99821, 728 ppbv, 0.9994 and 503 ppmv respectively. It shows that the two-component gas sensing system designed in this paper has a good linear response and high sensitivity, and plays an important role on the multi-component gas detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • An improved WMS-Y 1f method is suitable for the full range of concentration. • The interference of background gas is well eliminated under low modulation depth. • The relative errors are all less than 1%. At present, gas sensors are extremely susceptible to interference from background gases in the field environment, which leads to greatly reduced accuracy. For this reason, we propose an improved method of recovering integral absorbance (IA) using Y component of first harmonic to achieve accurate prediction of the full range of concentration (not reaching absorption saturation). This approach can eliminate the interference of background gas at a low modulation depth (m < 0.25). When the background gas is pure nitrogen and a mixture of nitrogen and carbon dioxide, the recovery effect of this method on methane is both close to the theoretical value when the background gas is air. The linear fitting coefficients for the methane concentration range of 2000–7000 ppm are all greater than 0.999. The prediction effect is satisfactory regardless of the background gas, with a relative error of less than 1%. In summary, this method has considerable application prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CH 4 /C 2 H 6 dual gas sensor using a single mid-infrared laser is developed. • The cross-interference of C 2 H 6 on CH 4 is eliminated. • High sensitivity, strong stability, fast response speed and simple system structure. Methane (CH 4) and ethane (C 2 H 6) dual gas sensor with low system complexity and strong stability is proposed. The correction method based on absorbance spectrum is applied, and the cross-interference of C 2 H 6 to CH 4 is eliminated. In the single gas concentration measurement, linear fitting is performed between the absorbance and concentration of CH 4 and C 2 H 6 , and the correlation coefficients of R2 = 0.99959 and R2 = 0.99994 are obtained respectively, which proves that the accuracy of the dual gas sensor is robust. In the dual gas concentration measurement, we carry out continuous measurement of five mixed gases and a long-term measurement of a mixture of gases, which verifies that our sensor has the fast response speed and strong stability. The minimum detectable column densities of 0.62 ppm·m for CH 4 and 0.1 ppm·m for C 2 H 6 are achieved, respectively. The CH 4 /C 2 H 6 dual gas sensor assisted by the correction method has high sensitivity and strong robustness to cross-interference, and has great potential for application in various scenarios. [ABSTRACT FROM AUTHOR]

Carbon monoxide and methane dual gas sensor with low system complexity and high stability is proposed in this study. A neural separator based on deep learning is developed to solve the cross-interference problem from the ultra-high spectral overlap between CO and CH 4 molecules. A large amount of simulated overlapping spectra of different concentrations CO and CH 4 are used to construct, train, tune and test the neural separator, instead of collecting data from onerous experiments. The linear fitting is performed between the predicted concentrations and preset concentrations of CH 4 and CO, determination coefficients of R2 = 0.99960 and R2 = 0.99301 are achieved respectively which proves the accuracy of the dual gas sensor is robust and greatly enhanced by the neural separator. In addition, the minimum detection limits of 120.86 ppm (CH 4) and 0.5 ppm (CO) are achieved in real-time simultaneous detection of CO and CH 4 overlapping environment. This is a successful attempt to apply deep learning method to tunable diode laser absorption spectroscopy (TDLAS) gas sensors to solve the problem of spectral cross-interference, which provides an alternative direction for the realization of simultaneous measurement of multi-component gases. • The dual gas sensor based on neural separator is developed. • The cross-interference problem with the ultra-high spectral overlap is solved. • The minimum detection limits of 120.86 ppm (CH 4) and 0.5 ppm (CO) are achieved. [ABSTRACT FROM AUTHOR]