Remote sensing of flammable and toxic gases via IPDA lidar with InGaAs/InP single-photon detector over C + L band.

An integrated path differential absorption lidar (IPDA) for remote sensing of flammable and toxic gases is proposed, which is based on a broadband-tunable external-cavity diode laser (ECDL) and InGaAs/InP single-photon detector (SPD). An ECDL can maintain a narrow linewidth of 10 kHz throughout the continuous frequency scanning process in the C + L-band (1520-1620 nm), thus allowing a single laser to satisfy the detection requirements of multiple gases. To eliminate the influence of background light, a programmable frequency- and bandwidth-tunable grating filter is designed to synchronously tune with the output frequency of the ECDL. A homemade multi-channel coupled InGaAs/InP SPD maintains high detection efficiency in the C + L-band, ensuring the remote sensing detection capability of lidar. Four gases-CO, H¹³CN, C₂H₂, and NH₃-with absorption lines spanning ∼45 nm in wavelength are selected to verify the multi-gas monitoring capability of the lidar. The intensity errors caused by erroneous photon counts and the non-linear frequency caused by the hysteresis effect of piezoelectric ceramic transducer are corrected to enhance the accuracy of absorbance spectra. The standard deviations of residuals between the experiment and single-peak fitting results for CO, H¹³CN, C₂H₂ are 0.22%, 0.54%, 0.39%, while the mean deviations are 0.19%, 0.44%, 0.29%, respectively. For the four-peak fitting of NH₃, those values are 0.55% and 0.38%, respectively. Continuous 12-hour monitoring of the path-integrated concentrations of the four gases is conducted to verify the stability and accuracy of the system. The mean deviations and standard deviations of CO, H¹³CN, C₂H₂, and NH₃ are 0.13%, 0.13%, 0.02%, 0.17%, and 1.07%, 1.68%, 1.21%, 0.67%, respectively.