Coherent population inversion in a four - level scheme

V. B. Krasovit︠s︡kiĭ, A.R. Linetskii

Olga A. Kocharovskaya, Paul Mandel, Yakov I. Khanin

Three- and four-level schemes of inversionless amplification with different types of coherent pumping is reviewed. Amplification without inversion between the 'bare' states is a result of population inversion between eigenstates of the density matrix. In particular, it can be achieved due to the coherent population trapping, i.e., effective removal from the interaction with the field a fraction of atoms at lower levels.

Klaas Bergmann, J. Martin, Bruce W. Shore

Jin‐Hui Wu, Huifang Zhang, Jin-Yue Gao

For a four-level atomic system with a doublet of closely spaced levels, we find that, owing to the coherence that results from the vacuum of the radiation field, population trapping at excited levels and probe gain with population inversion can be achieved with weak incoherent pumping. This gain is different from both the conventional lasing gain and gain without inversion in that there exists population inversion on probe transitions but the inversion is achieved by the vacuum-induced coherence.

Weicheng Chen

The coherence of a four-level Λ-type system with spontaneously generated coherence(SGC) is studied.With a weak probe and a strong coupling fields,whether the atomic system is on two-photon resonance or not,there is light without population inversion(LWI) on the probe field.On two-photon resonance,LWI is strengthened by SGC.On non-two-photon resonance,LWI can be controlled simply by adjusting the parameter of SGC and the two-upper-level separation.Meanwhile,the analytical solutions to the SGC parameter where LWI occurs are given in both cases.

Thomas Lindvall, Mikko Merimaa, Ilkka Juhani Tittonen