Fig. 5: Absorption coefficient (α) acquired from the multi-heterodyne dual comb spectroscopy spectra of the transition (J, K) = (12, 11 → 13, 12).
From: Quantum cascade laser based hybrid dual comb spectrometer
The transition has been acquired at methanol pressures of a 100, b 180 and c 300 Pa. Each point corresponds to the amplitude of the heterodyne beatnote (HBN) involved in the absorption, acquired in the down-converted radio frequency frequency comb spectrum. In these spectra the HBNs present a flat top, due to frequency instabilities. As a consequence, the uncertainty bars have been calculated as standard deviation on all the points of the HBN flat top. d The measured pressure shift is reported in the last panel, corresponding to a slope of −4.7(1.0) kHz/Pa. The retrieved center frequency for this transition is 3105511610(196) kHz. The uncertainty on the x-axis comes from the pressure gauge instrumental limit, while the uncertainty on the frequency center is due to the precision of the Voigt fits shown in the previous panels.
