Cavity-Enhanced Doppler-Broadening Thermometry via All-Frequency Metrology

We demonstrate Doppler broadening thermometry (DBT) with all-frequency-domain measurements. Using the R(10) transition of CO at 1567 nm in a high-finesse optical cavity (mode width 0.6 kHz), we resolve Doppler profiles with high signal-to-noise ratios across 2-17 Pa pressures. A global Voigt-profile analysis yields temperatures deviating by only -2.0±3.6  mK from calibrated thermometers, with systematic errors suppressed below 9 ppm. The results show negligible dependence on line-shape models when accounting for pressure effects, resolving a long-standing challenge in DBT. This approach establishes a new paradigm for quantum-based thermometry and provides a precision platform for testing molecular collision physics.