Measurement of atomic oscillator strengths in ytterbium by observation of coherent Rabi oscillations of excited-state populations

Two methods have been used to measure the oscillator strength of the transition between the ground and 17,992 cm level in XUYb. The first technique involves exciting the transition with a laser pulse that is nearly time-bandwidth limited, of uniform intensity, and has a reproducible shape from shot to shot. The population left in the excited state after the pulse varies sinusoidally with a period that depends on the integral over time of the electric field amplitude and the transition oscillator strength. These are the Rabi oscillations that are predicted by application of the Schrodinger equation to the two-level atom. The second method involves observation of the polarization rotation of a set of degenerate sublevels brought about by a light-shift laser. One sublevel (m/sub j/ = 0) of the J = 1 level at 17,992 cm is populated by a linearly polarized laser. A second copropagating light-shift laser, which is linearly polarized at an angle to the first laser, is tuned between 7.5 and 30 GHz off-resonance with the transition. The light-shift laser causes population to be promoted into the m/sub j/ = +-1 levels through the virtual J = 0, m/sub j/ = 0 level. Two linearly polarized photoionizing lasers photoionize the population only from the m/sub j/ = +-1 levels. The photoion signal oscillates cosinusoidally with a period that depends only on the integrated pulse intensity, the laser detuning, and the transition oscillator strength. Finally, polarization selectivity has been shown experimentally to allow selective photoionization of the odd isotopes of ytterbium using broadband lasers