Semi-Classical Calculations of Multiple Trajectories in High-Harmonic Generation

Abstract: The purpose of this thesis is to investigate the High-Harmonic Generation (HHG) process by simulating electron trajectories, and their resulting Extreme Ultra Violet (XUV) output. The HHG process is one in which a focused beam of infrared (IR) light can rival (in terms of intensity) the potentials of atoms, which makes tunnelling likely -- this sets off a chain of events resulting in an XUV pulse. The thesis utilises a semi-classical method in order to predict where one might look for further trajectories. This method is programmed into MATLAB in order to run simulations and investigate the results. The code allows for a deep-dive into different aspects of the process, including laser profile shape, laser properties (wavelength and intensity) and number of atoms within the beam. One of the conclusions of the thesis is the reaffirmation that finding the third trajectory is not simply a case of knowing what settings to apply, but moreso the principle that trajectories past the second are much less likely to be taken by electrons (even in a purely classical regime, before taking into account phenomena like Electron Wave Packet (EWP) spreading). The thesis also demonstrates an approximation of the HHG process to the tenth trajectory, where usually only up to the second is shown, which provides an interesting insight into how they are grouped around certain harmonics.