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arXiv:2601.10575

Electro-optic frequency comb Doppler thermometry

Sean M. Bresler, Erin M. Adkins, Stephen P. Eckel, Tobias K. Herman, David A. Long, Benjamin J. Reschovsky, Daniel S. Barker

physics.atom-phphysics.app-phphysics.opticsquant-phSubmitted Jan 15, 2026• Announced Jan 16, 2026
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Abstract

We demonstrate a Doppler thermometer based on direct optical frequency comb spectroscopy of an $^{85}$Rb vapor with a chirped electro-optic frequency comb (EOFC). The direct EOFC Doppler thermometer is accurate to within its approximately 1 K 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 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 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.

Journal reference
Optics Express 34, 12121 (2026)
DOI
10.1364/OE.590664
Comments
10 pages, 4 figures

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Abstract Based on the proposed theoretical model of a three-level system, the optical Bloch equations including the direct two-photon transition (DTPT) process using the optical frequency comb (OFC) were derived and the population distribution of particles in the upper states varying with the velocity of the atoms was obtained. Comparing to the resonance two-photon transition process, that population was increased by a factor of 1.4 without the Doppler shift, which is consistent with our previous experimental results. Simultaneously, the relationships between momentum transfers, and atomic velocity and pulse number were analyzed. When applied to a multi-level system it was found that the population of particles in the excited states increased by a few percentages. The novel approach of DTPT using OFC improved the utilization of comb teeth and atoms, increased the momentum transfer path, reduced the reachable Doppler temperature limit, and encouraged us to use OFC to cool multiple elements simultaneously through the DTPT process. By analyzing the Doppler temperature of 133 Cs and 87 Rb in one dimension, it was found that this process can lower a temperature below 100 mK and generate dipolar molecules 133 Cs 87 Rb via photoassociation, which provides us with a new tool to create dipolar molecules and to investigate their complex rovibrational spectra in ultra-cold chemistry.
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