|M.Sc Student||Diskin Tzvi|
|Subject||Quasi Phase Matching of High Harmonic Generation|
|Department||Department of Physics||Supervisor||PROF. Oren Cohen|
|Full Thesis text|
This thesis explores two noble concepts in the field of quasi-phase-matching of high harmonic generation. High harmonic generation of infrared and visible light is a useful process for production of extreme ultraviolet and soft x-ray radiation. In addition, high harmonic generation is used for producing attosecond pulses. The thesis handles two main challenges in the field of high harmonic generation, which are improving the efficiency and controlling the spectral (or temporal) properties of HHG. The thesis involves two parts that correspond to two papers. In the first part, a novel technique of quasi phase matching of only even order harmonics is proposed. In the second part, a technique of quasi-phase-matching using polarization beating of the driver is explored in details.
High harmonic spectrum of a quasi-monochromatic pump that interacts with isotropic media consists of only odd-order harmonic. Addition of a secondary pump, e.g. a static field of the second the primary pump, can result with generation of both odd and even order harmonics. This thesis describes a method for quasi-phase-matching of only even harmonics of the primary pump. Theoretical formulation and numerical results are presented. The results open the concept of selective control of the high harmonics spectrum using quasi-phase-matching which is based on symmetry arguments. The control of the spectrum results also to control of the temporal shape of the radiation. Specifically, even harmonics spectrum corresponds to attosecond pulse trains with stable carrier-envelope-phase and high repetition rate.
In the second part of the thesis, an analysis of a recently proposed quasi-phase-matching technique is reported. The technique uses polarization beating of the driver in birefringence medium, based on the phenomenon of reduction of the high harmonic generation process in elliptically polarized driver. A careful analysis shows that in addition to the polarization beating, the driver experiences phase modulation which decreases significantly the QPM efficiency. Theoretical formulation and numerical results are presented.