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High harmonic generation driven by few-cycle infrared fields in gases and liquids

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Title: High harmonic generation driven by few-cycle infrared fields in gases and liquids
Authors: Jarosch, Sebastian
Item Type: Thesis or dissertation
Abstract: High-order harmonic generation (HHG) in noble gases serves as the foundation of short-wavelength ultrafast optics and extensive research over the past 30 years has led to a comprehensive understanding of the involved generation processes. For the majority of theses studies, titaniumdoped sapphire lasers were deployed, emitting in the near infrared region at around 800 nm. Photon energies up to around 150 eV with unprecedented pulse durations down to hundreds of attoseconds were reached. However, the low conversion efficiency of the extremely nonlinear process is impeding a high flux of the short-wavelength radiation while intrinsic limitations in the generation process prevent higher photon energies at these driving field wavelengths. More recently, HHG was extended to well-ordered crystalline solids, both semiconductors and dielectrics, with continuing debate about the involved generation mechanism. A conclusive understanding of such high density targets is of particular interest, since it can potentially overcome the limit of the low conversion efficiency. This work describes the extension of high-order harmonic generation light sources to novel regimes with the aim to lift these restriction. In the scope of this work, three projects were taken forward. To detect and fully characterize the generated short-wavelength radiation, a high-order harmonic generation beamline was set up. A custom built and optimized charge detector system was developed and installed, enabling to determine the absolute photon flux of the harmonic emission. Deploying a short-wavelength infrared (1800 nm) few-cylce pulse with an excellent spatial and temporal beam quality and a high pulse energy of 750 μJ extended the accessible photon energy of the emitted soft X-ray radiation to the water window region (284 to 540 eV) and above. The emitted radiation was furthermore fully characterized, confirming its excellent spatial and temporal quality. Further, high-order harmonic generation in the liquid phase was studied, representing a largely unexplored generation medium. The liquid phase constitutes the missing link between a high density well-ordered solid target and an atomic or molecular gas, thus allowing to gain novel insights into the process of HHG. By scanning a number of laser and target parameters, the underlying mechanisms, including the extent of generation in liquid rather than surrounding gas, were investigated.
Content Version: Open Access
Issue Date: Mar-2019
Date Awarded: Sep-2019
URI: http://hdl.handle.net/10044/1/88008
DOI: https://doi.org/10.25560/88008
Copyright Statement: Creative Commons Attribution NonCommercial NoDerivatives Licence
Supervisor: Marangos, Jon
Tisch, John
Sponsor/Funder: European Union
Funder's Grant Number: Marie Sklodowska-Curie grant agreement No 641272
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses