Clumped isotope thermometry exploits the relative abundance of doubly substituted isotopologues to decipher the formation temperature of minerals. Here we present a promising approach based on mid-IR laser absorption spectroscopy for high-precision measurements of 13C18O16O, 12C18O2, 13CH3D, and 12CH2D2 isotopologues in CO2 and CH4. This optical approach offers rapid analysis on a 10-20 minutes scale, compared to hours or days needed for mass spectrometry. The currently reached sub-‰ precision is sufficient for the realization of an optical isotope thermometer for many geochemical applications.