High-order harmonic generation (HHG) is one of interesting phenomena which are originated from the interaction between intense laser pulses and atoms. It can not be explained in terms of perturbation theory, because the electric field of laser is similar to or stronger than the Coulomb electric field in the atoms.
There have been many attempts to explain HHG. Several theories could explain the several experimental results. Kulander carried out a theoretical analysis on HHG using time dependent Schrodinger equation calculations. As a result, this model could explain the properties of HHG at single atom level and show the plateau and cut off regions theoretically. On the other hand, Corkum proposed a semi-classical model that well explained the experimental and quantum mechanical results. Also Lewenstein proposed the quantum mechanical model of HHG based on the strong field approximation. He explained the HHG structure and offered the basis with respect to the propagation effect.
In this thesis, we focused on the analysis of HHG using the single atom calculations and the propagation effects, and investigated the characteristics of HHG while varying various parameters such as pulse duration, laser intensity, generating medium, laser wavelength, and gas density. We also considered the coherent sum of dipole moments to resolve the HHG. In particular using the Wigner distribution for a time-frequency analysis, we could interpret the chirping effect on the laser-pulse and a certain order of HHG.
