Phase Matching And Wave-front Manipulation In Nonlinear Optics

Phase matching is the core issue of nonlinear coupling process.The phase compensation technique,including birefringence phase matching,quasi phase matching,cavity phase matching,Fresnel phase matching etc.,play an important role in the frequency conversion process,which increase greatly the nonlinear conversion efficiency.The studies on these phase matching methods have attracted much attention for scientific research.Recently,beam shaping in microstructures is attractive as well.In the recent 10 years,several methods on the nonlinear beam shaping such as the local quasi phase matching,Fourier holography and the multiple slits technique are developed.Interesting functions have been realized with these methods.However these methods either are complicated or not universal.In this thesis,we developed a generalized reflective phase matching to study the phase compensation process and introduced the nonlinear holographic method to realize the nonlinear beam shaping.The main research parts are included as follows:1.We extended the Fresnel phase matching to the generalized reflective phase matching.The key concept is:the dispersion phase mismatching is compensated by use of the phase change of the parametric and the fundamental waves upon reflection.We demonstrated the concept on the metal-medium interface,and the obtained enhancement was 2 times the one without the metal-medium interface.We also tested the concept through a metal-CLN-metal micro-cavity;the enhancement was 4 times in total.With this method some bulk crystals which are unable to be fabricated with microstructures can be used for nonlinear frequency conversion.We predicted that compared with metal-medium interface a multilayered dielectric film could increase conversion efficiency further due to its lower reflective loss with much more flexibility of phase tuning feature.2.Using the nonlinear Huygens principle we proposed previously,we designed an optical superlattice for the polarization-dependent dual focused second harmonic generation.The focal points light distribution can be controlled by the polarization of the fundamental wave with the focusing effect as large as 14 times.Some other nonlinear processes(Cerenkov radiation,Raman-Nath diffraction,Bragg diffraction etc.)can also be explained with nonlinear Huygens principle.3.Based on the nonlinear Huygens principle,we extended the holographic method from linear optics to nonlinear optics.Using the interference of the nonlinear polarization wave and the harmonic wave,the wave-front information of the harmonic wave can be recorded in the form of the modulation of the nonlinear optical coefficient.This is an optical superlattice which acts as a nonlinear hologram.When illuminating the hologram with the fundamental wave,the harmonic wave would be reconstructed.With this method,we demonstrated experimentally the realization of the nonlinear Airy beam.The self-acceleration and self-healing properties were tested.We discussed the selectivity of nonlinear volume holography,-and evaluated its feasibility in nonlinear wave-front engineering.Second harmonic images such as "Batman" and letter "S" etc.were generated by the specially designed nonlinear hologram(optical superlattice).