Research And Application On The Nonlinearities Of Ferroelectric Domain Wall And Domain Inverison

Ferroelectrics, which have good nonliearities and can be inverted by external electrical field, have been widely used in nonliear optics. During the researches on ferroelectric domain and domain inversion, people found a lot of new characteristics of optical, electrical and mechanical properties on their interface—domain wall. Some of these new characteristics can be well explained by the first-priciple calculations and dynamic models. However, in the nonliear aspect, people are just starting to look at domain wall's nonliearities, and few report is found. Our work here are based on ferroeletric domain and domain inversion, aimed at domain wall's nonliearities. And we also make study on the electro-optical applications of domain inversion at the same time.After simple introduction of ferroelectrics, we review the common techniques to produce domain inversions, among which the poling at room temperature by external electrical field technique is the most widely used. We produce periodically poled and bulk domain inversion by this technique under lab environment. These two types of domain sturctures are the basis of our work here.Through a detailed anylasis of Cherenkov second harmonic generation (CSHG), we found significant enhancement of nonlinearities in domain wall. Based on this enhancement, we proposed a new method of scanning optical microscopy—reconstruct the domain walls by collecting the signals of CSHG in domain wall. This method has advantages of in situ, nondestructive, high resolution and 3-D reconstruction. We evaluated the width of domain wall is at the magnitude of 10nm and got a spatial angular resoluton of 10mrad.Domain wall can modulate the nonlinear polarization in it by locality. With the increasing of incident angle, the phase velocity of nonlinear polarization can be modulated faster. It affects the CSHG's ejecting angle. Based on domain wall's modulation effect, we predicted a CSHG in nonlinear material with anomalous dispersion and demonstrated it experimentally. Based on its principle, we named this effect nonlinear Smith-Purcell effect.Also based on domain wall's modulation effect, we designed the complete-phase-matching CSHG experiment. This is a new mechanism distinguished from quasi-phase-matching technique. The normalized conversion efficiency was even higher than that of quasi phase matching technique. It is because the giant enhancement of nonlinearities in domain wall and the complete-phase-matching mechanism. This scheme has application meaning, and can be used in laser systems.We proposed a method to control discrete spatial soliton and its collapse in periodically poled lithum niobate (PPLN) by electro-optical effect. Theoretical simulations showed that external electrical field can control the formation and collapse of soliton and change the energy distribution on the output surface. Experiment demonstrated that solitons can be formed in PPLN with z-directional electrical field. By changing the electrical field, one can control the soliton's formation and collapse easily.We also produced a quasi-volocity-matching electro-optic phase modulator in LiTaO3 crystal by using its large electro-optic coefficient. We made deep understanding on the theorectial design and producing technology. Modulator with different apertures are produced. By testing their modulation indices, we found these modulators can broaden the spectrum of the incidence effectively and rightly meet the design requirements.