Abstracts Category : Other

Frequency conversion of optical signals using coherentlyprepared media

by Ryan S Bennink

In the past decade, researchers have found that theoptical properties of a medium can be dramatically altered byoptically driving the medium into a coherent superposition of itsquantum states. Optical transitions from these states caninterfere, leading to optically induced absorption or transparency.Such "coherently prepared media" (CPM) typically have largewave-mixing susceptibilities without the resonant absorption thatusually accompanies large nonlinear susceptibilities. In certainschemes, a large material coherence can act as an oscillator whichscatters optical waves into modes of different frequency with highefficiency. Technologies based on this process could find usesranging from telecommunications to X-ray pulse characterization.The present work investigates the ability to coherently prepare anatomic vapor and to use that coherence to shift optical signalsfrom one frequency to another with high efficiency, bandwidth, andfidelity. </br>My theoretical studies of coherentpreparation include both simple and many-state systems. Whiletwo-state systems can display some coherent effects, coherenteffects are much more clearly displayed in three- and four-statesystems. A Bloch-sphere representation of Raman systems isdeveloped, which yields simple, easy-to-interpret graphicalsolutions and illustrates basic physical principles of coherentpreparation through simple formulas. The complications ofcoherently preparing a real vapor are also considered and discussedin detail. Experimentally, a pair of laser fields were used tocreate coherence between the 3S/ hyperfinelevels of sodium vapon Coherence-based optical effects includingtransparency, four-wave mixing, and Raman scattering were observed.Finally, coherence-induced Raman scattering was used to performfast (> 20 MHz), high-fidelity (> 99%) conversion of AM andFM optical signals from one carrier frequency to another. In spiteof these successes, the degree of coherence produced and theconversion efficiency were not as large as one would hope. My workconcludes with a discussion of the obstacles encountered inachieving large coherent effects in vapors and how they might beovercome.