Compact laser spectroscopy-based sensor using a transformer-based model for analysis of multiple molecules

Interest in the development of compact sensors that consume low energy is increasing day by day. This study reports, to our knowledge, such a novel sensor system that can analyze multiple molecules simultaneously with high sensitivity under ambient conditions (900 mbar and 300 K). To quantify molecules, a distributed feedback quantum cascade laser (DFB QCL) was combined with a compact multi-pass absorption (mpass) cell without the need for vacuum components, lock-in amplifier, or any electric filters. By using a transformer-encoder-based model, the noise level was reduced and the pressure-broadened absorption lines of the molecules were separated, narrowed (resolved), and displayed one by one. In this way, molecules can be quantified using pressure-broadened overlapping absorption lines under ambient conditions. To test our sensor system, CO2 and N2O molecules were used. Depending on the concentration values, SNR can be improved by up to 50 times. Better results are obtained at higher concentration values. Detection limits for N2O and CO2 molecules were determined to be 30 ppb and 180 ppm, respectively. The analysis time of molecules is around 80 ms.