Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE credits
In this thesis we extensively investigated numerically the phenomenon of ω-2ω gas high harmonic generation in Neon with different model calculations, and the second harmonic generation was also theoretically and experimentally examined for better predictions. We carried out experiments in order to determine the maximal conversion efficiency of second harmonic generation: the obtained energy conversion is 14%, what corresponds to ~3% intensity of the fundamental pulse. This corresponds to our SHG-calculations too.
The ω-2ω GHHG was simulated with different models. Firstly, several 1-atomic calculations were made with the Lewenstein-integral, and with the Saddle-Point Equations. The synchronization and the ratio of the fundamental and the SH pulse were examined in the ω-2ω GHHG. These results formed the basis to the deeper macroscopic simulations.
The extended macroscopic scans showed two distinct features of the ω-2ω GHHG. On the one hand, the one-atomic continuum-improvement can be transfered to 15 mbar-pressure gas cells with a precise adjustment. When Zirconium filter was applied, the transform-limited pulse durations could reach 74 as, which is a factor of 3 improvement compared to the GHHG without 2ω field. The exact value expected to be higher depending on the phase-structure of the radiation, which was not examined. On the other hand, when the medium was a high-pressure gas jet, the ionization gated GHHG spectra experienced a drastic amplitude-improvement with the SH field. Thus, while the pulse duration remained nearly the same, the intensity could reach even an 11-fold increment. In this case the transform-limited pulse duration is 66 as. The background of this phenomenon is still not investigated, however it is the first observation of this improvement to our knowledge.