Stable and unstable resonators within Fabry-Pérot optical cavities containing microlenses: laser arrays, low-coherence imaging, and fractal laser modes

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Steinforth, Austin William

Contributors dc:contributor

• Eden, James G
• Waldrop, Lara
• Dragic, Peter
• Fang, Kejie

• laser
• optics
• coherence
• imaging
• fractal
• microlens
• microsphere
• Fabry-Perot

Statement dc:rights

• Copyright 2022 Austin William Steinforth

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115764

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115764