Doctor of Philosophy
Mahi R. Singh
In this thesis, we study light-matter interaction in the contexts of coherent population trapping (CPT) and the ac Stark effect in nanoparticles embedded (doped) in two important classes of reservoirs -- photonic crystals and dispersive materials. These materials have gaps in their energy spectra and are studied widely due to their unusual optical properties and potential for novel applications. We consider that the reservoirs are doped with an ensemble of five-level nanoparticles, each with a single Λ core (consisting of a lower doublet and an upper energy level), which interact with both the host reservoir and external radiation fields. We have also included studies of cases where the nanoparticles interact with each other as well via dipole-dipole interaction (DDI), which is included in the mean field approximation. This only happens when the doping concentration is high (~ 1018 per cubic meter).
In studying CPT, we have developed a novel technique of optical switching by devising a system whereby the doped nanoparticles become stable against absorption from the radiation field(s) i.e. they switch to their ground states. We have confirmed the occurrence of CPT in both types of reservoir and have also identified a number of important contrasting features which have markedly different utilities. Most significantly, we have found that the strength of the DDI between the nanoparticles plays a very important role in determining the conditions required for CPT in both materials. In studying the ac Stark effect in photonic crystals, we have used an ensemble of five-level nanoparticles, each with a single cascade core [ladder configuration], both with and without DDI. We found that, in the ac Stark regime, resonance tuning of the transitions within the nanoparticles, in relation to the band structure of these crystals, offers a new mechanism for switching the nanoparticle system from an inverted to a non-inverted state. Specifically, a doped nanoparticle can effectively become transparent to any radiation field tuned to the probed transition. Under DDI, we found that the absorption in the system decreases with increasing DDI strength. These findings have very exciting potential for applications in optical switching.
Haque, Iftekharul, "A Study of Photon Trapping and the ac Stark Effect in Photonic Crystals and Dispersive Materials" (2015). Electronic Thesis and Dissertation Repository. 2670.