Optical Science and Engineering ETDs


Xiaozhen Xu

Publication Date



Laser filament provides scientists a powerful tool to promote and guide lightning discharge. An ultraviolet (UV) laser provides unique advantages due to a low threshold of filament formation as well as long propagation distance. However, a major bottleneck in conducting these experiments is the lack of a powerful yet stable laser source in the UV spectral range. Here, we developed a high power UV source suitable for laser filamentation studies in air. The system was optimized to produce < 300 ps, ~ 0.3J pulses at 266 nm. This corresponds to a peak power of ~1 GW, which is well above the critical power required for filament generation. The system includes four critical components: a single mode Nd:YAG oscillator, 6-stage amplifier chain, a pulse compressor and frequency conversion units. We optimized each component for maximum energy throughput with an emphasis on stability and reproducibility. At each stage, the optical output is characterized experimentally and compared to theoretical modeling of the corresponding physical processes. A number of technical innovations have emerged during the construction of the system. First, we invented a novel feedback-based cavity stabilization scheme for single-mode operation of the Nd:YAG oscillator. Our scheme eliminated mode beating in ~100% of the output pulses over a time scale of hours under noisy environments. Second, we developed a systematic optimization approach for high-energy pulse compression using stimulated Brillouin scattering. Our method achieved temporal compression of 40X in 532 nm with < 2% pulse-to-pulse fluctuation and elucidated the role of a number of overlooked parameters in the literature. We illustrated the application of the system with preliminary UV filamentation in air and laser-induced discharge studies. Future directions are discussed.

Degree Name

Optical Science and Engineering

Level of Degree


Department Name

Optical Science and Engineering

First Advisor

Diels, Jean-Claude

First Committee Member (Chair)

Brueck, Steve

Second Committee Member

Schwoebel, Paul

Third Committee Member

Arissian, Ladan

Document Type