Femtosecond-laser-induced plasma spectroscopy for high-pressure gas sensing: Enhanced stability of spectroscopic signal

Gas composition detection and analysis in high-pressure environments, such as those encountered in combustors, power plants, and planetary bodies, are important for scientific and engineering research. Conventional laser-based sensing using nanosecond (ns)-laser-induced breakdown spectroscopy (ns-LIBS) remains unreliable at elevated pressures because of the relatively high measurement uncertainty. To circumvent this problem, we propose to employ femtosecond-laser-induced plasma spectroscopy (FLIPS) to achieve a stable and reliable gas sensing at elevated pressures. A comprehensive study on the differences in the measurement quality of FLIPS and ns-LIBS for high-pressure nitrogen gas is conducted. The results show that the signal level and stability of ns-LIBS significantly decrease with the increase in pressure. In contrast, the signal level of FLIPS increases with the increase in pressure while maintaining the stability in the pressure range of 1-40 bar. In addition to the superior measurement stability, the FLIPS measurement provides a longer probe length (∼3 times compared to ns-LIBS) with a higher data acquisition speed (100 times compared to 10-Hz ns-LIBS).