Electro-optic frequency comb Doppler-broadening thermometry

We demonstrate Doppler-broadening thermometry based on direct optical frequency comb spectroscopy of an ⁸⁵Rb vapor with a chirped electro-optic frequency comb (EOFC). The direct EOFC Doppler-broadening thermometry measurements are accurate to within their approximately 1K statistical uncertainty. We experimentally compare direct EOFC spectroscopy with conventional Doppler spectroscopy using a single-frequency, step-scanned laser probe. Our results show that direct EOFC spectroscopy mitigates transit-induced optical pumping distortion of the atomic lineshape, which is the dominant systematic temperature shift in alkali atom Doppler-broadening thermometry. Optical Bloch equation simulations of conventional and direct EOFC Doppler spectroscopy confirm that EOFC spectroscopy can use higher optical power to reduce statistical noise without optical pumping distortion. Our results indicate that EOFC Doppler-broadening thermometry is a promising approach to realizing a primary thermometer with size and measurement rate sufficient for applications including pharmaceutical manufacturing and nuclear waste monitoring.