13CO2/12CO2 isotope ratio detection C2H2 detection GRIN fiber probe Ho:LuVO4 laser MgO:PPLN crystal PQS T1-995 TA1-2040 TDLAS TDLAS technique Tm a multi-reflection chamber absorption spectroscopy algorithm all-fiber laser broadband spectrum carbon dioxide monitoring chicken swarm optimization combustion diagnostic combustion sensing concentration prediction continuous-wave (CW) coupling efficiency deep-sea natural gas hydrate exploration design optimization detection limit diffuse integrating cavity direct absorption spectroscopy (DAS) femtosecond laser femtosecond laser electronic excitation tagging