High Harmonic Generation in Hollow Core Waveguides

University essay from Lunds universitet/Atomfysik

Abstract: The main goal of this thesis is to initiate a set of experiments on high-order harmonic generation (HHG) in hollow core waveguides and to verify a higher conversion efficiency of HHG in waveguides compared to classical HHG schemes. High harmonics are in this context electromagnetic waves generated by focusing laser light into a dilute noble gas. The frequency of the thereby generated waves is q times larger than the frequency of the driving laser. Compared to second harmonic generation or third harmonic generation where q is 2 and 3, q in case of HHG can theoretically be up to a hundred or more. The obtained radiation, which is in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) spectral regions, has a set of interesting properties which make it valuable for attosecond physics, classical spectroscopy and many more fields of physics. Classically, a so-called free focusing geometry is used to generate high harmonics. This represents schematically just focusing the laser beam into a gas jet. Due to the absorption length of the harmonics at atmospheric pressure the whole setup, from generation, to interaction, to detection must be placed in vacuum. Using hollow core waveguides for the generation process results theoretically in a higher generation efficiency and better gas confinement in vacuum environment, therefore a higher conversion efficiency is expected. Within this thesis a general theoretical foundation will be laid to understand the process of high harmonic generation and to explain the advantages of using hollow core waveguides. To underline the theoretical claims, a set of experiments is planned. The current status of the experiments is presented.

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