Research On Second And Third Order Nonlinear Optical Effect On The Interface Of LiNbO₃

In this thesis,we investigate various types of nonlinear optical phenomena generated on the interface of nonlinear ferroelectric crystal and their generation mechanism.In the first chapter,we simply introduce the nonlinear frequency conversion process in various nonlinear media,the phase-matching schemes and the interface nonlinear phenomenon.In the second chapter,we introduce various types of nonlinear phenomena generated on the interface of nonlinear crystal in our previous works.In the third,fourth and fifth chapters,we describe our innovative research results of nonlinear phenomenon generated on the interface of nonlinear crystal in depth.Due to the sadden change of non-linear coefficient on the crystal interface,it has a great influence on the nonlinear phenomenon compared with that in the bulk nonlinear crystal,and so there are many novel nonlinear optical phenomena that can be generated on the crystal interface.Thus,the nonlinear crystal interface will have great potential applications.In recent years,various types of nonlinear phenomena generated on the interface of ferroelectric crystal have been discovered.In our previous works,we also observed some new nonlinear optical phenomena,such as non-collinear second harmonic generation and nonlinear cherenkov radiation,which are generated on the interface of nonlinear crystal by the incident fundamental wave and reflected wave under anomalous dispersion condition.In this thesis,we investigate the angle,temperature and wavelength bandwidths of non-collinear phase matching second harmonic generation,which is generated on the inner surface of nonlinear crystal by incident and reflected waves.We theoretically give the non-collinear second harmonic coupled wave equations,and use the coupling wave model to simulate the non-collinear second harmonic generation.Furthermore,the measured bandwidths in our experiments result can be used to estimate the interaction length between fundamental wave and non-collinear second harmonic wave.By using the sadden change of non-linear coefficient on the crystal interface,we can obtain some innovate nonlinear phenomena by employing multiple laser beams to illuminate the interface of nonlinear crystal.In our experiment,we observe the enhanced nonlinear sum-frequency cherenkov radiation by using 1300 nm and 800 nm synchronized laser beams to illuminate the interface of nonlinear crystal.By using multiple laser beams to illuminate the interface of nonlinear crystal the semi-degenerate four-wave mixing can also be observed besides the nonlinear sum-frequency cherenkov radiation,which is generated by the incident fundamental wave,reflected wave and scattered wave.On this basis,we can do some further research on the more complex frequency conversion process by the interaction of multiple fundamental waves on the interface of nonlinear crystal.