High power ultrafast laser design and high-order harmonic generation in capillary discharge plasmas

2007 This thesis entitled: High power ultrafast laser design and high-order harmonic generation in capillary discharge plasmas written by David M. Gaudiosi has been approved for the Department of Physics Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. High power ultrafast laser design and high-order harmonic generation in capillary discharge plasmas Thesis directed by Profs. Chirped pulse amplification (CPA) has been used for over twenty years to generate high power, sub-picosecond laser pulses. In a chirped pulse amplifier, an ultrashort pulse is stretched, amplified, and compressed, usually using grating stretchers and com-pressors. Despite the low efficiency (50–60%) of grating compressors, this CPA scheme has remained virtually unchanged since the first demonstration [Strickland and Mourou, In the first half of this thesis, a novel amplifier design , based on downchirped pulse amplification (DPA), is presented. The DPA design utilizes a negative dispersion stretcher and a positive dispersion compressor, usually a block of transparent material. This design avoids many of the limitations, such as low efficiency and sensitivity to alignment, of traditional grating-and prism-based CPA systems. In addition to presenting the first demonstration of a DPA based amplifier system, the DPA scheme is combined with a simple, compact stretcher based on grisms to construct an ultrafast amplifier scalable to >40 kHz, a previously underdeveloped amplifier repetition frequency range. CPA systems have also enabled the study of high-field physics, specifically high-order harmonic generation. High-order harmonic generation is a process which generates extreme-ultraviolet radiation through the interaction of an intense laser field with a medium, usually a noble gas. Depletion of the neutral atoms, plasma defocusing, and energy loss due to ionization limit the laser intensity and ultimately the highest possible photon energy that can be generated. Using ions in a waveguide as the generating medium can minimize these limitations, extending the maximum photon energy. iv In the second half of this thesis, a method for generating high harmonic radiation from ions is demonstrated. A capillary discharge is used to preionize a low pressure xenon gas before a high intensity, ultrashort pulse is injected. The discharge generates ions and mitigates the plasma defocusing and ionization loss experienced by the ultra-short laser pulse, allowing for the generation of photon energies much higher than those previously observed in xenon. …