Stable and unstable resonators within Fabry-Pérot optical cavities containing microlenses: laser arrays, low-coherence imaging, and fractal laser modes
Steinforth, Austin William
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https://hdl.handle.net/2142/115764
Description
Title
Stable and unstable resonators within Fabry-Pérot optical cavities containing microlenses: laser arrays, low-coherence imaging, and fractal laser modes
Author(s)
Steinforth, Austin William
Issue Date
2022-04-15
Director of Research (if dissertation) or Advisor (if thesis)
Eden, James G
Doctoral Committee Chair(s)
Eden, James G
Committee Member(s)
Waldrop, Lara
Dragic, Peter
Fang, Kejie
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
laser
optics
coherence
imaging
fractal
microlens
microsphere
Fabry-Perot
Abstract
This work investigates Fabry–Pérot laser resonators that contain arrays of microlenses. The lenses locally stabilized the resonator, which enabled arrays comprising hundreds to thousands of independent microbeams to be generated from a single cavity of modest dimensions. When such beam arrays were used as illuminators for full-field imaging, they exhibited a reduced spatial coherence and increased angular diversity compared to a conventional, highly coherent laser. These factors resulted in speckle suppression that scaled as ~N^(−1/2), where N is the number of independent beams in the array. The short duration (< 10 ns) and high pulse energy (≥8 mJ) of the array emission made it possible to image targets that moved at speeds up to 300 m/s with high resolution and no motion blur, as well as targets that were far from the source and camera (≥5 m, at present), and when optically dense fog intervened the beam path. Regions in between the lenses behaved as unstable resonators and were found to exhibit fractal characteristics in their transverse electric field profiles. Families of modes were simulated for two specific resonator configurations, and higher-order fractal modes were generated experimentally for the first time. The fractal dimension of each mode was found to evolve as the field propagated through the cavity.
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