Dinc, CemCemDincNitzsche, PonkanokPonkanokNitzscheGoldschmidt, JensJensGoldschmidtSchmitt, KatrinKatrinSchmittWöllenstein, JürgenJürgenWöllenstein2025-06-172025-06-172025https://publica.fraunhofer.de/handle/publica/48872610.5162/SMSI2025/A1.4This work presents an approach to detect and measure the specific isotopic ratio of the stable methane isotopes 12CH4 and 13CH4 using a high-finesse cavity within an Optical Feedback CEAS system. The development of this approach is ongoing with the aim of precisely measuring the isotopic ratio under atmospheric conditions in the mid-infrared (MIR) spectral region around 3001.2 cm-1, where the absorp-tion lines of the two stable isotopologues are located and well separated under a pressure of 40 mbar enabling the simultaneous measurement of both within a spectral range of 1 cm-1.enOptical Feedback CEASMethane isotopic ratioAbsorption spectroscopyMIR environmental sensorGreenhouse gasconference paper