STUDY OF COHERENCE EFFECTS IN MULTILEVEL ATOMIC SYSTEMS

Abstract

Electromagnetically induced transparency (EIT) causes the cancellation of the absorption of a weak probe field in the presence of a strong control field for a medium composed of a multilevel system. Therefore, the optical response of the medium can be manipulated owing to the ability to induce coherence using the laser fields. EIT transparency is associated with a normal dispersion while enhanced absorption results in an anomalous dispersion at the line center. This thesis concentrates on the various factors affecting the EIT resonances in multilevel systems for Rubidium atom. The effect of wavelength mismatching is explored in an inverted-Y type system with mismatching factor varying up to two orders of magnitude. In an inverted-Y type system, composite of and subsystems, the mixing of Doppler-free system and Doppler-broadened system cause splitting of EIT transparency window and enhanced absorption is observed on both sides of the line center. Thus both type of light propagation behavior, sub- as well super-luminal is observed for mismatched states. On slightly detuning the system, switching from sub- to super-luminal light propagation is observed. A four-level 􀀀 type system is examined to study coherence effects and EIT along with electromagnetically induced absorption (EIA) phenomena are probed. In the inverted-Y type system, absorption vanishes at the line center. However, in the 􀀀 system enhanced absorption is observed at the line center. In 􀀀 system, iii transparency switches into absorption when the third field is applied. These complex multilevel systems can be employed for optical switching applications. Further, a comparative study of five- and seven-level systems with wavelength mismatching, the close proximity of hyperfine levels and different polarization combinations of the optical field is also presented. Narrowing of EIT resonances in presence of an external magnetic field is explained for a three level system. This thesis has the aim of exploring EIT in multilevel systems and various parameters which notably change its behavior. One of the themes to emerge from our analysis of multilevel systems is the study of light propagation and switching from sub- to super-luminal on varying the chosen parameters.