טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAverbukh Vitali
SubjectMultiphoton Processes Induced by High Intensity Fields
DepartmentDepartment of Chemistry
Supervisor Professor Emeritus Nimrod Moiseyev


Abstract

The connection between the classical chaos and regularity and the extent of the high harmonic generation plateau is studied using monochromatically driven rigid rotor model. In addition to high harmonic generation, the rotor is found to exhibit a classically forbidden transition called dynamical tunneling. We demonstrate that the only “chaotic” quasienergy states of the model give rise to the harmonic generation spectra with an extended plateau. In the high frequency − high intensity regime classical harmonic generation spectra are shown to approximate well the quantum mechanical ones. The classical theory of harmonic generation in this regime provides a simple analytical expression for the probability to emit the nth harmonic of the external field frequency, usually possessing a maximum, so that a single harmonic peak dominates the spectrum.

We consider the dynamics of the selective high harmonic generation by the systems possessing a high-order spatio-temporal symmetry. It is shown that the dominant contribution to high harmonic generation by the studied class of systems comes from the bound − bound transitions. The molecular cutoff position depends linearly on the electric field strength and the molecular dimensions. This allows to reach higher harmonic orders by employing larger targets. We extend the method for the formulation of selection rules for high harmonic generation spectra beyond the dipole approximation in order to describe properly the generation of harmonics by single-walled carbon nanotubes interacting with a circularly polarized laser field. Our time-dependent tight-binding calculations demonstrate that the carbon nanotubes can be excellent systems for a selective generation of high harmonics, up to the soft X-ray regime.

We describe an experimentally feasible scheme for the preparation of giant-dipole states of atoms interacting with crossed electric and magnetic fields by trapping the relative motion of  the core and the electron in the outer potential well.