| In this thesis, coherent population trapping (CPT) is studied in two real-world systems: atomic sodium vapor and a quantum well structure. A series of spectroscopic studies were carried out in the atomic system to understand how CPT behaves in a non-idealized environment. In addition, a feasibility study is carried out to seek a solid state environment to facilitate the design of practical devices based on the process of CPT.; The first system used to study CPT is sodium vapor (the "real atom"). Even though sodium is a multi-level system, the spectral features and the parameters that govern them are found to be similar to those of the idealized three-level Λ system. For example, in both the idealized model and the actual atomic system, the ground state decoherence rate determines the width of the resonance as is demonstrated experimentally. The inclusion of Doppler broadening and propagation effects, and the impurities in the vapor, are found to weaken the strength of the CPT resonance. The presence of additional levels, which can either be virtual or real, permits additional concurrent processes to occur that enrich the spectrum. These concurrent processes are coherent Raman scattering, other wave mixing processes, crossover resonances, and optical pumping. Coherent Raman scattering can even invert the induced transparency feature of CPT into an induced absorption feature.; In spite of these complications, CPT has great potential for technologically advanced applications, with the example of frequency conversion being demonstrated here. As a medium for these applications, semiconductor systems are more practical than atomic sodium.; The second system studied is a quantum well structure (the "artificial atom"), designed to mimic a Λ configuration suited for observing CPT. Novel use of various aspects of band engineering and structure design is utilized to achieve such a configuration. An AlAsSb/InGaAs/AlGaAsSb ternary-quaternary alloy system is used to create an Island well structure. By employing intersubband transitions only within the conduction band, a single carrier-type system is achieved. It is predicted that CPT can still be observed even with the added complexity of this semiconductor system. |
