Dispersion-like lineshape observed in cavity-enhanced saturation spectroscopy of HD at 1.4 µm
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Updated: Dec 10, 2025

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Abstract:
Precision measurement of ro-vibrational transitions in the electronic ground state of the hydrogen molecule can be used to test quantum electrodynamics and also to determine the dimensionless proton-to-electron mass ratio. Saturation spectroscopy of the 2-0 overtone transitions of hydrogen deuterium (HD) were measured with three cavity-enhanced spectroscopy methods. With a sensitivity at the 10-13cm-1 level, we revealed a dispersion-like lineshape instead of a conventional Lamb "dip," which explains the significant discrepancy among previous independent measurements. The spectra can be fit well by using the Fano profile. Centers of R(1) and R(3) lines were determined as 217 105 182 111 (19)(240)kHz and 220 704 305 234 (20)(240)kHz, respectively.
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