| This work presents the use of a set of principles of quantum coherence to a set of related topics. The binding theme is the idea that this fundamental approach can be used to improve known effects by eliminating harmful noise and absorption, and can make new effects possible. The basic atomic physics that is the foundation of the rest of the dissertation is developed, including the most useful analytic and numerical techniques.; In the second chapter, the principles of the quantum coherence and the techniques of atomic physics are used to present improvements to two devices. The first is Faraday-rotation magnetometry at high density and temperature, which is presented here from concept to experimental results. The second is the free-electron laser without inversion (FELWI), with a new approach to the drift region design which is not only easier to apply, but also produces much greater gain than seen before.; There has been a thread of work in fundamentals of quantum mechanics throughout this research, and the third chapter of the dissertation presents work in two topics: quantum eraser and bell-basis measurements. |
