Absolute frequency metrology of buffer-gas-cooled molecular spectra at 1 kHz accuracy level
Roberto Aiello, Valentina Di Sarno, Maria Giulia Delli Santi, M. De Rosa, I. Ricciardi, Paolo De Natale, Luigi Santamaria Amato, G. Giusfredi, P. Maddaloni
Abstract
Abstract By reducing both the internal and translational temperature of any species down to a few kelvins, the buffer-gas-cooling (BGC) technique has the potential to dramatically improve the quality of ro-vibrational molecular spectra, thus offering unique opportunities for transition frequency measurements with unprecedented accuracy. However, the difficulty in integrating metrological-grade spectroscopic tools into bulky cryogenic equipment has hitherto prevented from approaching the kHz level even in the best cases. Here, we overcome this drawback by an original opto-mechanical scheme which, effectively coupling a Lamb-dip saturated-absorption cavity ring-down spectrometer to a BGC source, allows us to determine the absolute frequency of the acetylene ( ν 1 + ν 3 ) R(1)e transition at 6561.0941 cm −1 with a fractional uncertainty as low as 6 × 10 −12 . By improving the previous record with buffer-gas-cooled molecules by one order of magnitude, our approach paves the way for a number of ultra-precise low-temperature spectroscopic studies, aimed at both fundamental Physics tests and optimized laser cooling strategies.