Research On Linear Cherenkov Radiation In Ferroelectric Domain Walls

Since the technology of quasi-phase matching has been realized,the structures of artificial ferroelectric domains walls are becoming common.So our research focus on the nonlinear effects in domain walls.We think that the light with different frequencies can be coupled with each other,then we assume that the light with same frequency but different polarization states may be coupled.Nonlinear Cherenkov radiation plays an important role in detecting the internal structure of the ferroelectric domain.During the research,we found that the lattice symmetry of the domain walls has been broken via bulk media.Then we predict the existence of polarization state coupling on the domain walls.This paper includes the theoretical analysis and experimental research.The research focuses on the polarization state transition process based on the domain walls,and the emitted light satisfy the Cherenkov condition.So we called the linear Cherenkov radiation(LCR).This article focuses on the new phenomenon that LCR can be stimulated on the domain walls,which is the first time that this phenomenon has been observed in the domain wall structure.We theoretically construct the theoretical model of the domain walls stimulating the emitted light and obtain the expression of it,including both the situation of single domain wall and periodic domain walls.Then we theoretically verify the emitted light is LCR according to the coupled wave equation.The effects of some parameter on the intensity of LCR intensity are also discussed in our paper.Experimentally,according to the birefringence effect of birefringent crystal,we can obtain two kinds of polarization states.Then we experimentally demonstrated the generation of such LCR in the periodically distributed domain walls.The modulation effect of domain walls on linearly polarized waves is analyzed in our manuscript.The domain walls localize the linear polarization wave nearing the wall rather than spreading along the incident direction,resulting in the phase velocity increasing.We also obtain the linear susceptibility matrix of the domain wall by the phenomenon of LCR,and the matrix also reflects the symmetry properties reduction of the domain wall,which is consistent with theoretical prediction.The LCR is difficult to stimulated in the bulk medium,but it is relatively easy to be observed in domain walls.That means,the LCR carries the structural information of the domain walls.