Research On The Method And Characteristics Of Wavefront Restoration Based On Cherenkov Harmonics Of Nonlinear Interface

Wavefront is able to carry a lot of physics characteristics,such as atmospheric disturbance,internal and surface structure information of objects,organic texture and so on,thus wavefront detection techniques are always widely employed in various areas.With more requirements of functions and performance proposed by people,more new ideas and techniques are introduced into wavefront detection researches,leading whose feasibility and accuracy improved gradually.Combining nonlinear optics with wavefront detection,for example,has become one direction for researchers.This paper begins with the theory of nonlinear frequency conversion,making a brief instruction of frequency conversion at nonlinear crystal boundary and nonlinear Cherenkov radiation.Then we further discuss the method to reconstruct wavefront based on Cherenkov-type harmonic generation at the nonlinear boundary.We study the influence of several factors and the reconstruction results.Nonlinear boundary is a kind of physical boundary with hopping nonlinear coefficient.At these locations,symmetry has been broken,new reciprocal lattice vector appears,and the stimulated polarized wave is constrained on the crystal boundary.The above characteristics all make a difference in the polarization and harmonic generation process.Hence,in some way nonlinear boundary is superior to bulk material for harmonic generation.We carry on corresponding research,and find out that no matter in total-reflection-assisted non-collinear phase-matching,or in Cherenkov-type harmonic generation,nonlinear boundary always help to improve conversion efficiency markedly.Besides,through theoretical analysis,we notice that,Cherenkov-type harmonic generation owns more concise wavefront correlation with fundamental wave than common phase-matching process.Therefore,we made numerical computing of wavefront characteristics with Matlab,and verify which in experiment.We also discussed and synthesized the relationship of wavefront between fundamental wave and second-harmonic generation as well as a series of related factors.Based on these,we studied the reconstruction of fundamental wave.The main innovations are as follows:1.We propose a method exploiting Cherenkov-type harmonic generation based on nonlinear boundary.This method requires no special angle-matching or quasi-phase-matching,or crystal alignment.The selections of both material and incident way are flexible;and the auto-segregation of harmonic generation and fundamental wave makes it easy to take a measurement.2.This method provides broadband doubling-frequency that can realize crystal inner surface measurement.Through setting reference light,surfacedistribution of nonlinear boundary can be obtained in this way.