Control of absorptiion and dispersion of light by coherence in a atoms and molecules

Abstract

The objective of this thesis is to explore the effects of the quantum coherence towards the precise control of the manipulation of the interaction between the atomic or molecular systems and the electromagnetic fields. This leads to the maneuvering of the optical response of the medium. More precisely, the present study is devoted to the coherence phenomena designated for the manipulation of dispersion together with absorption in an anisotropic as well as an isotropic medium. Such a control is attributed to the quantum interference created by the control field. Many novel optical phenomena such as electromagnetically induced transparency, coherent population trapping, lasing without inversion, saturated absorption techniques, enhancement of refractive index, manipulation of group velocity etc. are consequences of the quantum interference and coherence. Coherence can also be generated by vacuum that arises due to the quantum interference between the spontaneous emission pathways. The present study deals with the application-oriented aspects of the these novel optical phenomena. Further, besides the manipulation of linear response, quantum coherence plays a vital role for the control of nonlinear response, as well. Several nonlinear phenomena such as saturable and reverse saturable absorption along with the optical bistability have been explored. The theoretical investigations have been done in the framework of semiclassical picture of the light-matter interaction, while the dynamics of the constituents of the medium is studied using density matrix formalism.