THE ROLE OF HYPER-RAMAN TRANSITIONS IN THE RADIATION SPECTRUM OF A STRONGLY DRIVEN 2-LEVEL ATOM

Numerical results are presented on the spectrum of the light scattered into the vacuum modes by a two-level atom driven by a strong ramped f ield of frequency smaller than the natural atomic frequency. The atten tion is focused on the role of the hyper-Raman part of the spectrum, w hich is shown to decrease dramatically with increasing ramp time. It i s suggested that this may explain lack of experimental observation of the hyper-Raman lines. For zero ramp time, the numerical intensity of both high-order harmonics and hyper-Raman peaks is shown to agree sati sfactorily with previous analytical predictions except in the region o f overlap of the two series of peaks. This lends support for the sugge stion that the plateau in the spectrum is related to quantum-mechanica l interference between high-order harmonics and hyper-Raman processes. There is also good agreement between the numerical amplitude of the p lateau and previous analytical predictions. A physical mechanism for t he cut-off frequency which terminates the plateau, based on approximat e energy conservation in hyper-Raman transitions, is presented and is shown to be in agreement with present numerical and previous analytica l results.