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Authors: Beckwitt, Kale
Keywords: nonlinear optics
quadratic media
second-order media
non-stationary processes
phase compensation
spatiotemporal solitons
multidimensional solitons
effective Raman
non-instantaneous processes
cascaded quadratic processes
Issue Date: 15-Jul-2004
Abstract: This thesis presents experimental and theoretical investigations of processes involving the propagation of short optical pulses in second order nonlinear materials. Since pulse propagation in these materials involves the nonlinear coupling of fields at different frequencies, the dynamics are rich, supporting a wide variety of nonlinear processes. In the limit that an effective Kerr nonlinearity is produced, we demonstrate compensation for cubic nonlinearities in space and time with negative Kerr-like quadratic phase shifts. Self-focusing and self-phase modulation from Kerr nonlinearities typically limit the energy and beam quality from high power lasers, and their compensation allows for significant improvements in both parameters. We next present theoretical results on the formation of optical solitons in quadratic media --- fields of light that propagate stably (or ``breath'' periodically) due to a robust balance between linear broadening and nonlinear confinement. We are interested in multidimensional solitons in space and time, with the eventual goal of producing ``light-bullets:'' fields confined in all transverse dimensions. Spatiotemporal solitons provide a natural system in which to observe new effects related to soliton propagation and interactions, with direct applications to optical signal transfer and processing. Recent experiments by our group demonstrate quadratic solitons in time and one spatial dimension, but are not extendible to three-dimensions due to the material systems used. We theoretically demonstrate a quadratic system in which light-bullets are possible and point a way to their observation. This is the only currently recognized optical system where stable light-bullets are predicted. Finally, we present a new type of cascaded interactions: nonlinear \emph{frequency} shifting in the limit in which temporal walkoff between the nonlinearly coupled fields significantly affects their propagation dynamics. Previous applications of cascaded nonlinearities saw temporal walkoff as detrimental and found ways to mitigate its effects. We develop a theoretical model for cascaded interactions with significant walkoff and show that non-instantaneous nonlinear responses are possible, producing controllable nonlinear frequency shifts with strong analogs to Raman-scattering in cubic materials. These frequency shifts are analyzed theoretically and experimentally and their applications from low energy frequency shifting for optical communications to compression of high energy pulses are discussed and demonstrated.
Description: Committee members: Frank W. Wise, Albert Sievers, and Tomas Arias
Appears in Collections:Cornell Theses and Dissertations

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