Saturation Processes in Nonlinear Media Modeled by Four-Level Configuration with Coincident Absorption and Emission Bands

Abstract

The four-level model is used to study the nonlinear media with coincident absorption and emission bands in both principal (S0S1) and excited (T1T2) channels. The excitation of molecules occurred by two light elds: radiations with intensity I12 at frequency ω0 tuned at the centre of absorption band of principal singletsinglet channel and radiations with intensity I34 at frequency ω tuned at the centre of absorption band of excited triplettriplet channel. The monotonic dependence of phase response of media in both principal and excited channels and the saturation processes are studied theoretically and numerically for four-level model.

Saturation in the principal (excited) channel of four-level medium as an effective two-level configuration

“…The saturation intensity of radiation for a four-level medium under the action of radiation with two frequencies (ω 0 , ω) can be written as follows: (1) for radiation in the principal (singlet-singlet S 0 -S 1 ) channel, and ------------------------= (2) for radiation in the excited (triplet-triplet T 1 -T 2 ) channel [15], where: and p ij is the total probability of spontaneous and irradiation transitions in the i-j channel, the Einstein coefficients B 12 (ω 0 ) and B 21 (ω 0 ) are determined at radiation frequency ω 0 in the principal singlet-singlet channel, and B 34 (ω), B 43 (ω) are determined at the radiation frequency ω in the excited triplet-triplet channel [19].…”

“…The tuning frequency of various radiation and the bleaching conditions for dye solutions were taken into account and compared in some cases with a two-level model. In addition, for these configurations, the possibility of controlling nonlinear effects in a given channel (principal or excited) by radiation in another channel was studied [16][17][18][19][20].…”