Electromagnetically Induced Transparency In Λ-Shaped Three And Four Level Systems

On the basis of quantum mechanics and absorption spectrum experiments, this thesis presents a theoretical study of interaction betweenΛ-shaped level systems and lasers or microwave fields. The investigations are carried out in the frequency domain where steady state properties are examined. Firstly, using an idealΛtype three-level double resonance configuration and assuming the two lower levels arising from hyperfine structure, an extremely narrow electromagnetically induced transparency (EIT) feature is obtained and its spectral width is investigated as a function of both coupling and probing laser intensities. The power broadening behaviors of the EIT feature are studied over a broad range of laser intensity and the results show that at low laser intensities limit, the EIT width has a dependence on the coherence relaxation rate of hyperfine transition. The dependence of the EIT width on the couple laser intensity shows that at relative low couple laser intensity there is a quadratic dependence of the EIT width on the couple laser Rabi frequency and at large couple laser intensity the EIT resonance evolve into the well known dynamic Stark splitting and its width has a linear dependence on the couple Rabi frequency. And the dependence of the EIT width on the probe laser intensity shows that at relative low probe laser intensity, the EIT width remains constant, but strong probe effects lead to power broadening of the EIT feature. Then the effect of a microwave field on an EIT feature is studied. In addition to these two laser fields, there is a microwave field which drives one of the two lower levels of theΛtype three-level system to another hyperfine level. The microwave field drives the hyperfine transition that shares a common level with the probed optical transition and the EIT feature is studied as a function of microwave field frequency and intensity. Our results show that the presence of a microwave field can dramatically modify the EIT feature. When microwave is resonant with the hyperfine transition, the EIT feature can be split into two EIT features. When it is off resonant with the hyperfine transition, it causes a frequency shift of the EIT feature, reminiscent of the well-known light shift effect. By controlling the microwave field intensity and detuning, we can continuously vary the spectral position of the EIT window, thus realize EIT frequency tuning. In addition a physical account of the splitting of EIT is given in terms of a dressed state picture.