Fig. 2: Example of the spectra recorded with our instrument in the deep cryogenic regime.
From: Cavity-enhanced spectroscopy in the deep cryogenic regime for quantum sensing and metrology
The 1 - 0 S(0) line of the H2 molecule at 2.22 μm is recorded at several temperatures from 4.9 K to 7.8 K, which are far below the H2 melting and boiling points where the vapour pressure strongly depends on temperature. The horizontal axis is shifted to the unperturbed position of the transition, ν0. The red lines are the fitted line-shape models that include both Doppler broadening and relevant collisional effects (we used the SDHC profile55,56 with β correction57 included). Note the log scale on the vertical axis. The pressures and temperatures indicated in this figure are the values determined optically. See sections ‘Realization of the primary SI units at deep cryogenic temperatures’ and ‘Hydrogen phase diagram’ and Table 1.
