Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Juliet T. Gopinath

Second Advisor

Mark E. Siemens

Third Advisor

Robert R. McLeod

Fourth Advisor

Thomas R. Schibli

Fifth Advisor

Scott A. Diddams

Abstract

Lasers have revolutionized a wide range of industries, including communications, sensing, and imaging. This thesis uses spatial and temporal control of laser beams to improve laser sources. In the first part, a fast and simple spatial beam characterization technique is demonstrated for measuring the M2 beam propagation parameter. This variable-focus method uses only a focus-tunable liquid lens and a CCD camera; there are no moving parts. The technique is also extended to the characterization of twisting general astigmatic laser beams that carry orbital angular momentum in their spatial phase structure. The study of optical orbital angular momentum (OAM) is a maturing field with developed applications in communications and imaging and potential applications in sensing. The second part of this thesis explores the parameters governing the generation of OAM in optical fibers by addition of the fiber eigenmodes. Average OAM tunable between +1 and -1 ħ/photon is demonstrated in two-mode polarization maintaining optical fiber. Varying the phase and coherence between the fiber modes independently controls both the OAM and the spatial beam profile. In addition, simulations of fiber optic sensors based on OAM show the potential for temperature measurements with high resolution of 0.0085 degrees Celsius.

Whereas spatial control enables tight focusing and OAM, temporal control is useful for nonlinear optics applications. Temporal compression of laser light enables compact sources of high-peak power pulses for multiphoton imaging. In the third part of this thesis, a miniaturizable semiconductor-based pulsed laser source is demonstrated for two-photon excitation fluorescence microscopy. Time-lens pulse compression reduces the laser pulse duration to ~3 ps at 976 nm. The repetition rate is electronically variable between 66.67 kHz and 10 MHz. Two-photon imaging of oligodendrocytes at up to 600 μm depth in mouse brain tissue is demonstrated with the miniature laser system.

Available for download on Friday, July 31, 2020

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