• weak quadrupole S(2) 2-0 line in self-perturbed D2 is measured • collisional line-shape effects and energy of this rovibrational transition are calculated • the velocity-changing collisions are handled with the hardsphere collisional kernel • the experimental and theoretical pressure broadening and shift are consistent within 5 • we observe 3.4 sigma discrepancy between experimental and theoretical line position

We describe a high sensitivity and high spectral resolution laser absorption spectrometer based upon the frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) technique. We used the Pound-Drever-Hall (PDH) method to lock the probe laser to the high-finesse ring-down cavity. We show that the concomitant narrowing of the probe laser line width leads to dramatically increased ring-down event acquisition rates (up to 14.3 kHz), improved spectrum signal-to-noise ratios for weak O(2) absorption spectra at λ = 687 nm and substantial increase in spectrum acquisition rates compared to implementations of FS-CRDS that do not incorporate high-bandwidth locking techniques. The minimum detectable absorption coefficient and the noise-equivalent absorption coefficient for the spectrometer are about 2×10(-10) cm(-1) and 7.5×10(-11) cm(-1)Hz(-1/2), respectively.

An experiment enabling extremely high signal-to-noise ratios in the measurement of spectral line shapes is described. This approach, which combines high-bandwidth locking of a continuous wave probe laser and the frequency-stabilized cavity ring-down spectroscopy technique, enables long-term signal averaging and yields high-resolution spectra with a relatively wide dynamic range and low detection limit. By probing rovibronic transitions of the 16 O 2 B band near λ = 689 nm, exceptionally precise measurements of absorption line shape and line position are demonstrated. A signal-to-noise ratio of 220 000 and a minimum detectable absorption coefficient of 2.4 × 10 −11 cm −1 is reported, which corresponds to the lowest line intensity measurable by this setup of approximately 1.3 × 10 −30 cm −1 /(molecule cm −2 ). Careful analysis of the data revealed a subtle line-shape asymmetry that could be explained by the speed dependence of the collisional shift. The demonstrated measurement precision enables the quantification of systematic line-shape deviations, which were approximately 1 part in 80 000 of the peak absorption. The influence of slowly drifting etaloning effects on the precision of the line-shape analysis is discussed. How this method can enable experiments that address a number of fundamental physical problems including the accurate optical measurement of the Boltzmann constant and tests of the symmetrization postulate is also discussed.

Line shapes and intensities of self-broadened O ) band transitions measured by cavity ring-down spectroscopyWe present high-resolution line-shape and line-intensity measurements of self-broadened Otransitions measured using the frequency-stabilized cavity ring-down spectroscopy technique under relatively low pressure conditions. We give line-shape parameters describing collisional broadening and shifting, and we treat line narrowing in terms of Dicke narrowing or the speed dependence of collisional broadening. We indicate the importance of the line-narrowing effect which, if neglected, changes the experimentally determined collisional broadening coefficients by up to 48%. We report measured line intensities with relative uncertainties below 0.7% and compare these measurements to published data.