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We have studied the temporal profile of photon-echo signals generated by combined gated cw and pulsed dye-laser excitation of the inhomogeneously broadened, 555.6-nm absorption line of (174)Yb vapor. We find that the echo profile is, after time reversal, essentially identical with that of the first excitation pulse. We give a new analysis of this effect. Since time-reversed pulse reproduction should also occur in inhomogeneously broadened solid samples, and since we observe time-reversed reproduced pulses up to 4% as intense as the input pulse, this effect may have important applications in optical signal-processing systems.

Polarization spectroscopy makes use of the polarization dependence of the nonlinear interaction between two laser beams in a gaseous medium.The laser-induced optical anisotropy is calculated using a rate equation approach, and the effect of this anisotropy on a polarized probe beam is derived.The method is useful for Doppler -free spectroscopy, for similification of molecular spectra, and for relaxation studies.A comparison with other Doppler -free saturation spectroscopy methods shows an advantage in signal -to -noise for polarization spectroscopy.Recent high resolution experiments with hydrogen, molecular sodium, and nitrogen dioxide are presented.

Two-step polarization-labeling spectroscopy of diatomic molecules is described. Formulas for relative transition intensities are derived, and their use in determining angular momenta of molecular states is discussed. The experimental apparatus and procedure used to identify twenty-four new 'S,+, 'Il, , and '3, states in Na, are deScribed. The states are identified as low-lying members, n = 3 to 14, of several molecular Rydberg series, and the dependence of their properties on principal quantum numbers is shown. These results are extrapolated to yield constants for the ground state of Na, +.

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