Cavity-enhanced saturation spectroscopy of molecules with sub-kHz accuracy

Abstract

Saturation spectroscopy is frequently used to obtain sub-Doppler measurement of atomic and molecular transitions. Optical resonant cavities can be used to enhance the effective absorption path length, and the laser power inside the cavity as well to saturate very weak ro-vibrational transitions of molecules. Three different cavity-enhanced methods, cavity enhanced absorption spectroscopy, cavity ring-down spectroscopy, and noise-immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS), were compared by measuring the Lamb dip of a C 2 H 2 line at 1.4 µm using a cavity with a finesse of 120000. The center of the line was determined by different cavity-enhanced methods, each giving a sub-kHz (δν/ν≈10 −12) statistical uncertainty. The sensitivity and precision of different methods were analyzed and compared. As demonstrated in this study, the NICE-OHMS method is the most sensitive one, but more investigation on the systematic uncertainty is necessary before its application in metrology studies toward a sub-kHz accuracy.

Comb coherence-transfer and cavity ring-down saturation spectroscopy around 1.65 μm: kHz-accurate frequencies of transitions in the 2ν3 band of 12CH4

“…16 However, only recent advances in laser technology and introduction of high sensitivity detection techniques, such as cavity ring-down spectroscopy (CRDS), make saturation spectroscopy attractive for a wide range of problems in high precision molecular spectroscopy and optical metrology. 6,17–27…”

Precision spectroscopy of molecular hydrogen

“…High-finesse cavities used in cavity-enhanced spectroscopy not only enhance the detection sensitivity but also significantly increase the intra-cavity laser power, which is necessary for saturation spectroscopy measurement. Various cavity-enhanced saturated absorption spectroscopy techniques 128–131 have been employed to measure saturated spectra (Lamb dips) of weak molecular ro-vibrational transitions.…”

Dipole saturated absorption modeling in frequency modulation spectroscopy: Dealing with a Gaussian beam, resonance narrowing

“…The analysis of the resonances shape has been mainly obtained by varying the value of the collision rate, an alternative to the gas pressure, because of the lack of well-established proportionality between the collision rate against the gas pressure under saturation conditions: specifically, self-pressure broadening coefficients available in the literature can exhibit a pressure dependence (factor 2 to 3) for methane [4,40,10,41], for carbon dioxide [42,43], for iodine [44], for water [45], and for acetylene [9,46,47]. The dependence of the resonance shape with the mean transit-time rate is also discussed.…”