Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm

Abstract

Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C2H2 between 7167 and 7217 cm−1, using a frequencycomb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers. We measured the absolute center frequency of sixteen lines belonging to the 2ν3 + ν15 band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a “V”-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 2 and 13 kHz. This is over three order of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene.

Lamb-dip ro-vibrational spectroscopy of buffer-gas-cooled acetylene

“…In conclusion, by applying the Lamb-dip SCAR technique to a buffer-gas-cooled molecular sample, we have determined the absolute frequency of a selected ro-vibrational transition with a fractional uncertainty of 6 × 10 −12 . In fact, by ranking with the highest accuracy levels obtained so far with long-standing room-temperature methodologies [20,21,22,23,24,25], our achievement marks the birth of frequency metrology on buffer-gas-cooled molecular spectra. Being straightforwardly extendable to many species in different spectral regions, our method will be especially useful for those molecules (even simple ones) whose room-temperature spectrum is congested [26].…”

Absolute frequency metrology of buffer-gas-cooled molecular spectra at the 10-12 accuracy level

“…In this configuration, we address the acetylene (ν 1 +ν 3 ) R(1)e ro-vibrational line at 6561.0941 cm −1 in a 20-K cell specimen, demonstrating absolute line-center frequency measurements with an overall (statistical + systematic) fractional uncertainty as low as 6 × 10 −12 . In fact, by equaling the highest accuracy levels obtained so far with long-standing methodologies involving room-temperature samples [25][26][27][28][29][30], our achievement marks the birth of frequency metrology on cold spectra.…”

Absolute frequency metrology of buffer-gas-cooled molecular spectra at 1 kHz accuracy level

“…In this configuration, by way of example, we address the acetylene (ν 1 + ν 3 ) R(1)e ro-vibrational line at 6561.0941 cm −1 in a 20-K cell specimen, demonstrating absolute line-center frequency measurements with an overall (statistical + systematic) uncertainty as low as 1.2 kHz (6 × 10 −12 in fractional terms). In fact, by ranking with the highest accuracy levels obtained so far with deep-rooted methodologies involving room-temperature cell samples, either in the Doppler-limited 33,34 or Doppler-free regime [35][36][37][38][39][40] , our achievement finally opens a metrological perspective to the spectroscopy of buffer-gas-cooled molecules.…”