Nondegenerate 4-wave mixing enhanced by the ac Stark effect

Thesis (Ph. D.)--University of Rochester. College of Engineering and Applied Science. Institute of Optics, 1982. This thesis was digitized by the Institute of Optics in 2014 and was determined to have lapsed into the public domain. If you are the author and have questions about the digitization of your work, please contact Kari Brick, Graduate Program Coordinator for the Institute of Optics, at kbrick@ur.rochester.edu. Other contact information for the Institute is available at http://www.optics.rochester.eduThe existence of resonant enhancement in nonlinear optical mixing due to the ac Stark effect is reported. It is predicted theoretically and shown experimentally that there is substantial gain for a four-wave mixing process in which the optical fields are in resonance with the frequencies of an atomic system modified by an intense optical field. The ac Stark effect results from the oscillation of the atomic population inversion at the generalized Rabi frequency. This frequency has two contributions which add in quadrature: the beat frequency between the unperturbed atomic resonance and the optical field; and the Rabi frequency which is the rate at which the population inversion would be forced to oscillate by stimulated emission and absorption if the beat frequency was zero. It has been found by probing with a weak optical field, that the atom's original levels split into two new levels. These two new resonances are separated from the driving field's frequency by the generalized Rabi frequency. When a single probe field is tuned to one of these new resonances, it is attenuated and when tuned to the other resonance, it is amplified by the three-photon effect. It is shown here that when both fields are simultaneously present, a parametric coupling between them can cause both waves to grow. The theoretical description of this four-wave mixing process is obtained by first solving the density matrix equations of motion for the atomic response. These density matrix elements are then used as source terms in the coupled-wave equations. Analytic expressions are obtained for the parametric gain for the two weak fields. These expressions show substantial gain for the weak fields at the ac Stark split levels (Rabi sidebands). Experimental observation of the Rabi sidebands is reported. It is also shown here that the often observed conical emission surrounding the output of an intense laser beam after it traverses an atomic vapor is caused by Rabi sideband generation in tile presence of self-focusing. Self-trapping of pulsed laser radiation is also reported