Research On Modulating Nonlinear Harmonic Radiation By Structured Fundamental Wave

Since the creation of lasers,nonlinear optics has been widely studied in all fields of science.Nonlinear harmonic radiation such as nonlinear Cherenkov radiation has also attracted the attention of researchers in the nonlinear frequency conversion process.The nonlinear harmonic radiation has been found there is a significant enhancement of the domain structure in previous researches.Therefore,in the previous study,the nonlinear harmonic radiation was mainly modulated by different domain structures of nonlinear photonic crystals(NPCs),such as the domain structure modulated into a ring,rectangle,hexagonal,whereas SHG in NPCs is fundamentally restricted by their predesigned structures and has the complexity of the crystal fabrication process.We introduced the concept of structured FW into tailoring the nonlinear harmonic radiation process and this study provides a new way of dynamically tailoring the nonlinear harmonic radiation.It is more flexible to modulate the FW itself.In this paper,we theoretically simulated and experimentally investigated the nonlinear harmonic radiation with structured FW,whose phase was periodically modulated.Firstly,we study the nonlinear Cherenkov-type SHG with structured FW in NPC.Based on the nonlinear coupled wave equation,we derived the formula of the nonlinear Cherenkovtype SHG involved the structured light.In experiment,the Cherenkov-type SHG with different parameters of the structured FW was investigated.The experimental results are in good agreement with the theoretical analysis.This study provides a method of dynamically tailoring the Cherenkov-type SH wave.At the same time,we discuss the influence and function of structured FW in other nonlinear frequency conversion processes such as assisted-scattering second harmonic rings,and find there are potential application in other nonlinear frequency conversion processes.The results provided a new method for tailoring nonlinear harmonic radiation process with structured FW,which can control more freedom of FW,and is also more flexible than modulated nonlinear crystal without the need for complicated fabrication processes.The field also has potential applications in other nonlinear harmonic radiation processes.