The cavity-ringdown technique is applied to measure Rayleigh extinctions of Ar, N 2 , and SF 6 in the 560 -650-nm region at 294 K. It is shown that experimental and calculated Rayleigh scattering cross sections agree within an experimental uncertainty of 1% (for SF 6 , 3%).  2000 Optical Society of America OCIS codes: 290.5870, 290.5840.A century ago Lord Rayleigh formulated a theory of light scattering by ideal gases that not only explained the molecular origin of atmospheric scattering and the blue color of the clear sky but also provided a quantitative expression for the amount of light scattered.

0͒ band of the 16 O 18 O, 16 O 17 O, 18 O 2 , 17 O 18 O, and 17 O 2 isotopomersof oxygen. The weak magnetic dipole transitions around 760 nm were observed using cavity-ring-down absorption spectroscopy. The positions of over 340 lines are presented together with ͑re-͒ analyses of the rotational constants. We discuss the importance of these data in view of tests of the symmetrization postulate in 16 O 2 and present a sensitivity scale of 13 orders of magnitude that could be practical for future test experiments.

The intensity and noise properties of decay transients obtained in a generic pulsed cavity ringdown experiment are analyzed experimentally and theoretically. A weighted nonlinear least-squares analysis of digitized decay transients is shown that avoids baseline offset effects that induce systematic deviations in the estimation of decay rates. As follows from simulations not only is it a method that provides correct estimates for the values of the fit parameters, but moreover it also yields a correct estimate of the precision of the fit parameters. It is shown experimentally that a properly aligned stable optical resonator can effectively yield monoexponential decays under multimode excitation. An on-line method has been developed, based on a statistical analysis of the noise properties of the decay transients, to align a stable resonator toward this monoexponential decay.

This paper reports on the absorption of molecular oxygen in the region of the A-band near 760 nm under atmospheric conditions relevant for satellite retrieval studies. We use pulsed laser cavity ring-down spectroscopy with a narrow bandwidth laser and use pressure scans to increase the accuracy of the measured oxygen extinction coefficients. Absolute binary absorption coefficients in minima between absorption lines of the A-band spectrum have been measured and tabulated. We use the so-called adjustable branch coupling model including line mixing to calculate the magnetic dipole absorption in order to determine the contribution of collision induced absorption. The line mixing model has been optimized such that the collision induced absorption spectrum is smooth.

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