We report the enhanced optical transmission in the coherent, off-resonant excitation of Rydberg atom gases at room temperature via a two-photon process. Here thermal resonance-enhanced transparency (TRET) is induced when the detuning of the two lasers is adjusted to compensate the atomic thermal-motion-induced energy shifts, i.e., single- and two-photon Doppler shifts. We show that the atomic velocity is mapped into the transmission of the probe fields, which can be altered by independently and selectively exciting different velocity groups through sweeping the detuning. The maximal transmission in TRET is about 8 times higher than that under electromagnetically induced transparency (EIT). Utilizing the TRET effect, we enhance the sensitivity of a Rydberg microwave receiver to be $28.7{\mathrm{nV}\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$, ultimately reaching a factor of 2.1 of the EIT case. When atoms of separate velocity groups are excited simultaneously by multiple laser sets of different detuning, the receiver sensitivity increases with the number of laser sets. Our study paves the way to exploit light-matter interaction via the TRET, and contributes to current efforts in developing quantum sensing, primary gas thermometry, and wireless communication with room-temperature atomic gases.

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• Atomic spectra
• Light-matter interaction
• Rydberg gases