|Ph.D Student||Barak Freedman|
|Subject||Nonlinear Wave Interactions in Periodic and Quasiperiodic|
|Department||Department of Physics||Supervisor||? 18? Segev Mordechai|
|Full Thesis text|
· The first experimental observation of optical spatial shock-waves. The shock waves consist of two coupled kink and antikink beams that remain locked to each other throughout propagation. These coupled shock-wave pairs move undistorted at angles that fall outside their original angular sector of propagation, hence they exhibit superluminal propagation (in matter). These effects are driven by energy transfer between the tail regions of optical spatial shockwaves, resulting in a change in the propagation direction.
· A new method of optical waveguiding, called "Grating Mediated Waveguide". The new method relies on Bragg diffractions from a 1D grating that gives rise to waveguiding in the direction normal to the grating wave vector and arises from cross-phase modulation. The waveguide structure consists of a shallow 1D grating that has a bell- or trough-shaped amplitude in the confinement direction.
· I have used optical induction to create nonlinear photonic quasicrystals and show the first observation of wave dynamics in quasi-periodic optical lattices, including experiments on linear “discrete” diffraction from various lattice sites, lattice solitons, and experiments on nonlinearly interacting quasi-periodic lattices. These experiments show how an interacting photonic quasicrystal with a dislocation can heal itself through nonlinear interactions.
· Phasons and phason strain are a special type of excitations unique to structures lacking periodicity, but with long range order (incommensurate structures). Quasicrystals are a special case of this type of structures. I studied defect dynamics arising from these excitations in interacting nonlinear photonic quasicrystals, and demonstrated the first quasi-periodic lattice whose structure incorporates phasons but no phonons at all. I demonstrated experimentally that phasons survive longer than phonons, and that nonlinear interactions in photonic quasicrystals can reduce the phason density within the structure.