ULTRAFAST FIBER LASERS ENABLED BY HIGHLY NONLINEAR PULSE EVOLUTIONS
Ultrafast lasers have had tremendous impact on both science and applications, far beyond what their inventors could have imagined. Commercially-available solid-state lasers can readily generate coherent pulses lasting only a few tens of femtoseconds. The availability of such short pulses, and the huge peak intensities they enable, has allowed scientists and engineers to probe and manipulate materials to an unprecedented degree. Nevertheless, the scope of these advances has been curtailed by the complexity, size, and unreliability of such devices. For all the progress that laser science has made, most ultrafast lasers remain bulky, solid-state systems prone to misalignments during heavy use. The advent of fiber lasers with capabilities approaching that of traditional, solid-state lasers offers one means of solving these problems. Fiber systems can be fully integrated to be alignment-free, while their waveguide structure ensures nearly perfect beam quality. However, these advantages come at a cost: the tight confinement and long interaction lengths make both linear and nonlinear effects significant in shaping pulses. Much research over the past few decades has been devoted to harnessing and managing these effects in the pursuit of fiber lasers with higher powers, stronger intensities, and shorter pulse durations. This thesis focuses on less quantitative metrics of fiber laser performance, with an emphasis on furthering the versatility and practicality of ultrafast sources. Much of this work relies on the calculated use of strong fiber nonlinearities, turning conventionally-undesirable phenomena into crucial tools for enabling new capabilities. First, the generation of femtosecond-scale pulses from much slower, more robust sources is investigated, conferring not only reliability advantages but also a fundamentally greater scope for repetition rate tuning. Next, prospects for fiber lasers operating at wavelengths far from any gain media are explored. By leveraging optical parametric gain alongside chirped-pulse evolutions, energy and bandwidth generated at one wavelength can be efficiently converted to another, while keeping the pulse's phase and compressibility intact. Both the scaling properties and the underlying theoretical considerations of this approach are discussed. Prospects for realizing optical parametric sources in birefringent step-index fibers are then studied. By using the polarization modes in a telecom-grade fiber to obtain phase-matching, new wavelengths can be generated while eschewing photonic crystal fiber and its inherent practical disadvantages. Finally, more speculative ideas for future work along these themes are discussed.
Physics; Optics; Nonlinear; fiber; Laser
Wise, Frank William
Strogatz, Steven H.; Schaffer, Chris
Ph.D., Applied Physics
Doctor of Philosophy
dissertation or thesis