Absorption And Dispersion Properties In Quantum Interference Systems

The main purpose of my thesis is to investigate various effects related toquantum interference, such as electromagnetically induced transparency, highindex of refraction without absorption, and amplification without inversion, invarious laser-matter interaction systems. The systems we considered includeatoms and semiconductor quantum well structures, involving both transientprocess and steady state. My thesis is consisted of six parts:I. Effect of vacuum-induced and microwave-induced coherence on the transient process in atomic systems In this part, we investigate the transient properties in three level Λ - andV-type atomic systems with vacuum-induced coherence, and in amicrowave-driven three level Λ -type atomic system, respectively. We foundthat, the vacuum-induced and microwave-induced coherence both greatlymodify the transient behavior of the probe field. The interference term makesthe transient behavior of the probe field becomes quite sensitive to the relativephase Φ of the applied fields. Different values of Φ lead to differentfeatures of the transient behavior, and the transient absorption can be 195completely eliminated just by choosing proper values of the relative phase. The considered three-level Λ -type atomic system is shown in Fig. 1. Thetwo lower levels are closely lying, when the two dipole moments arenonorthogonal, cross-coupling happens between the two decay channels fromthe upper level to the ground doublet and results in a kind of quantuminterference, named vacuum-induced coherence. In this system, a strongcoherent field is applied as coupling field, and a weak field is applied as probefield. Properly arrange the polarization of the applied fields so that one fieldacts on only one transition, i.e., εrc ⊥ dr13 , εrp ⊥ dr23 . Fig.1 A three-level Λ -type atomic system with vacuum-induced coherence In the framework of semi-classical theory, the density matrix equationsincluding the vacuum-induced coherence terms are dependent on the relativephase Φ of the applied fields, from which we can obtain the time-dependentnumerical solutions of the gain-absorption coefficient in the transient process. By considering the time evolution of the gain-absorption coefficient (shownin Fig. 2), we found that when η = 0 (solid curve), the probe field shows 196oscillatory behavior versus time, i.e., the probe laser exhibits periodicamplification and absorption. When η = 1, i.e., when the VIC effect isincluded, the transient property is greatly altered, and it exhibits different...