Transient Susceptibility of Two-Level System Irradiated by Two Monochromatic Radiations

Abstract

It is investigated how a two-level system under the influence of strong monochromatic radiation responses to weak monochromatic radiation in a transient state. The general solution of the equation of motion for the density matrix is obtained within the linear approximation with respect to the ratio of the amplitude of the weak radiation to that of the strong radiation. It is shown that for the frequency difference of the two radiations smaller than the inverse of transverse relaxation time (|ω−ω′|T₂<1), the amplitude of the nutation in transient susceptibility to the weaker radiation becomes very large compared with the amplitude in the opposite situation; |ω−ω′|T₂\gtrsim1. The first peak of this amplitude is proportional to 1⁄(ω′−ω), where ω′ and ω are the frequencies of the weak and strong radiation respectively. Therefore, the transient amplitude of the susceptibility becomes very large as ω′→ω as far as the linear approximation is valid. This giant susceptibility is originated in a transient Raman Process.