Event
Ph.D. Dissertation Defense: Andrew Goffin
Monday, April 1, 2024
10:00 a.m.
ERF 1207
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Dissertation Defense
Name: Andrew Goffin
Committee:
Professor Howard Milchberg, Chair/Advisor
Professor Phillip Sprangle
Professor Julius Goldhar
Dr. Eric Rosenthal
Professor Ki-Yong Kim, Dean's Representative
Date/Time: Monday, April 1, 2024 at 10 AM
Location: ERF 1207
Title: Applications and Dynamics of Long-distance Laser Filamentation in Air
Abstract:
Femtosecond laser pulses with sufficient power will form long, high-intensity light channels called filaments. Filaments form due to nonlinear self-focusing in the medium focusing (or “collapsing”) the pulse until collapse is arrested. For near-infrared pulses in air, collapse arrest is instigated by photoionization and the resulting plasma defocusing. The dynamic balance between plasma defocusing and nonlinear self-focusing allows high-intensity filament propagation over long distances, much longer than possible with typical beam sizes and linear focusing due to diffraction. The filament consists of a high intensity ~200 µm diameter core (Rayleigh length ~ 4 cm), where plasma is generated, and a much larger, lower intensity reservoir, where there is no ionization. The reservoir drives energy into the core through self-focusing, and as such the filament length is proportional to the Rayleigh length of the reservoir.
In this thesis, atmospheric filaments are used for a variety of applications and are studied in detail. In particular, the ability of filaments to clear fog through acoustic wave generation is studied by measuring the displacement of single water droplets near a filament. Air waveguides are generated from multifilamenting rings to guide follow-on beams in two limiting cases: (1) long distances, up to nearly 50m, with a finite waveguide lifetime and (2) shorter distances, but without waveguide dissipation in a “quasi-steady-state” regime. In each case, a recipe is given to generate longer distance guides and achieve quasi-steady-state guiding. Finally, the impact of pulse duration on filamentation dynamics is studied, and it is shown how an optimal pulse duration is chosen for long-distance filamentation in atmosphere.
