Strong field effects in high harmonics generation from dielectric crystals
File(s)
Author(s)
Kowalczyk, Katarzyna Marianna
Type
Thesis
Abstract
High harmonics generation (HHG) is an ultrafast, strong-field frequency upconversion process, which is a source of sub-fs pulses spanning into the extreme ultraviolet (EUV) regime. In a solid target, the harmonic signal is a result of sub-cycle electron motion within the electronic band structure of the crystal and therefore is known to be an excellent probe for intrinsic physical properties of crystalline solids.
This dissertation delivers experimental results on HHG in wide-bandgap dielectric crystals in the transmission geometry. The results link the electron trajectory picture to the experimental observables. In the scope of this work, two experimental projects are discussed.
To study the strong-field nonlinear propagation of an ultrafast beam through a wide bandgap dielectric, a z-scan technique: measurement of the non-linear refraction and non-linear absorption was performed on bulk 200 μm Magnesium Oxide (MgO) crystal. The non-linear refractive index of MgO was determined, for the first time under fs laser beam, to be n2(780 nm)=1.1±0.2 x10 -20 m2/W. An in situ spectral measurement also allowed for benchmarking of solid-sample nonlinear propagation calculations. The calculations enabled modelling of the propagation of the driving field up to the last nanometres of the sample which generate the observed EUV harmonics. Using a transverse spatial coherence model of harmonic generation, the intricate spatiospectral structures present in the far-field projection were justified with a single electron trajectory picture as a direct result of the complex phase and spatial structure of the driving electric field...
This dissertation delivers experimental results on HHG in wide-bandgap dielectric crystals in the transmission geometry. The results link the electron trajectory picture to the experimental observables. In the scope of this work, two experimental projects are discussed.
To study the strong-field nonlinear propagation of an ultrafast beam through a wide bandgap dielectric, a z-scan technique: measurement of the non-linear refraction and non-linear absorption was performed on bulk 200 μm Magnesium Oxide (MgO) crystal. The non-linear refractive index of MgO was determined, for the first time under fs laser beam, to be n2(780 nm)=1.1±0.2 x10 -20 m2/W. An in situ spectral measurement also allowed for benchmarking of solid-sample nonlinear propagation calculations. The calculations enabled modelling of the propagation of the driving field up to the last nanometres of the sample which generate the observed EUV harmonics. Using a transverse spatial coherence model of harmonic generation, the intricate spatiospectral structures present in the far-field projection were justified with a single electron trajectory picture as a direct result of the complex phase and spatial structure of the driving electric field...
Version
Open Access
Date Issued
2024-09-26
Date Awarded
01/02/2025
License URL
Advisor
Matthews, Mary
Sponsor
Royal Society (Great Britain)
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)