Demonstration of filament-guided electrical discharges from a high average power 1 kHz picosecond laser
Date
2023
Authors
Dehne, Kristian A., author
Rocca, Jorge, advisor
Marconi, Mario, committee member
Brewer, Samuel, committee member
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Abstract
The atmospheric propagation of ultrashort, high energy laser pulses is of interest for applications including remote sensing, directed energy, and the guiding of lightning. In this thesis, the filamentation of high energy picosecond laser pulses at repetition rates up to 1 kHz is demonstrated and the guiding of electrical discharges in air at high repetition rates is studied. The design and performance of the diode-pumped Yb:YAG chirped pulse amplification (CPA) system utilized for this experiment is also described. Diode-pumped solid state lasers in a CPA layout have emerged as the modern choice for the generation of high pulse energies at high repetition rates. For the work presented in this thesis, a high average power diode-pumped Yb:YAG laser system utilized for filament formation is de- tailed. The compact CPA system, which combines a room temperature regenerative amplifier and cryogenically cooled Yb:YAG amplifiers, results in compressed pulses of < 5 ps duration with up to 1.1 J of energy at 1 kHz repetition rate. This record Joule-level 1 kHz repetition rate picosecond laser (average power output of more than 1 kW) has enabled the results described herein. The application of this high average power Yb:YAG system for producing laser guided electrical discharges is the main focus of this thesis. The compressed output pulses from the Yb:YAG laser induce filamentation in air, resulting from the counterbalance between Kerr self-focusing and plasma refraction defocusing. The hydrodynamic response of the atmospheric air results in a density depression of similar geometry to the filament. The result is a preferential path which both triggers and guides electrical discharges. The majority of previous laser-guided discharge studies have been conducted at repetition rates of 10 Hz, where the medium completely recovers before the next laser pulse arrives. This thesis reports on the physics of laser filament-guided electric discharges in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of ∼7 ps duration at repetition rates up to 1 kHz. A breakdown voltage reduction of up to 4.2 X was measured and determined to result primarily from the perturbation caused by a single laser pulse, with cumulative effects playing only a secondary role. A current proportional to the laser pulse energy arises as soon as the laser pulse arrives, initiating a high impedance phase of the discharge channel evolution. Full breakdown, characterized by impedance collapse and the onset of high current conduction, occurs 100s of ns to a few μs later. The gaps between the filamentary plasma channel and the electrodes are observed to play a role in the delay between arrival of the laser pulse and the onset of a discharge. The breakdown voltages measured for 100 Hz and 1 kHz repetition rates are shown to be nearly equivalent. This is consistent with the results of interferometric analysis which shows that the filament formed by a single laser shot causes a deep density depression up to 75%, compared with the 20% density depression measured 10 μs prior to the arrival of a laser pulse in a sustained 1 kHz sequence. The physical insight gained from this work on the formation of laser filament-guided discharges in air at 1 kHz repetition rate can be expected to contribute to their use in applications.
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Embargo Expires: 05/26/2024
Subject
filament
discharge
laser