In conditions of frequency tuning of the exciting radiation, the energy threshold, and spectral characteristics of the infrared induced three-photon scattering (IR ITPS) of light in rubidium vapor are investigated. It is established that induced cascade transition arising as a result of multiphoton ionization of the atoms has a significant influence on the occurrence of this process. The features of IR ITPS excitation are investigated for the case where the conditions of both two-photonn (5${^2}$S$_{1/2}$—5$^{2}$D$_{5/2}$) and single-photon(5${^2}$S$_{1/2}$ — 5$^{2}$ P$_{3/2}$)resonance are simultaneously satisfied. It is observed that, on approaching the single-photon resonance,the reduction in excitation threshold and icrease in energy of the scattered radiation that is expected from theory is not observed, but instead the completely opposite picture; the excitation threshold rises and the energy decreases.This contradiction between theory and experiment is explained.
Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia
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