Research On Nonlinear Optical Phenomena And The Applications Of Ferroelectric Domain Surface

Phase matching is a key factor in the nonlinear frequency conversion process,which impacts much on the conversion efficiency, and in recent years, new type ofphase matching schemes are constantly emerging, including not only newconfiguration, but also combination of the traditional phase matching schemes withnew technologies. Nonlinear Cherenkov radiation, with automatically longitudinalphase matching, is able to generate second harmonic but not limited by thewavelength. It is not limited by the acceptance bandwidth in that of birefringence orquasi-phase matching schemes. New features make ferroelectric domain walls a newresearch hotspot in recent years. It has been shown that relative to the bulk medium,the nonlinear crystal interface has become a new functional material, which can beused to yield new nonlinear process with potential applicative value. This paper willmainly study on nonlinear Cherenkov radiation at crystal interface and other newphase-matching schemes.In this paper, we clean up the basic definition, classification, and the newfeatures of ferroelectric domain wall as a new functional material, and analyze theenhanced nonlinear Cherenkov radiation at lithium niobate domain walls bytheoretical calculation, including Ginzburg-Landau-Devonshire (GLD) theory andfirst-principles calculation. Through the electric field poling technique at roomtemperature, we fabricated the single domain wall and domain wall arrays, whichprovided facilities for studying of domain walls.By using ferroelectric crystal interface, it can break the velocity threshold offundamental wave, resulting in nonlinear Cherenkov radiation in anomalousdispersion conditions. This work breaks the traditional knowledge on Cherenkovradiation, and reveals the novel actions of nonlinear crystal interface in the nonlinear process. These interfaces include not only the domain wall, crossing which thesecond-order nonlinear coefficient changes from+1to-1, but also the crystal surfacewhere the second-order nonlinear coefficient changes from+1to0. The coupled wavetheoretical model can explain the enhanced nonlinear Cherenkov radiation at theinterface to a certain extent. In addition to Cherenkov second harmonic generation,Cherenkov sum frequency and Cherenkov high-order harmonic generation bymultistep cascading are also conducted in-depth researches.Enhanced nonlinear Cherenkov radiation at a single interface can be consideredas a basic nonlinear process, on the basis of which there is more complex frequencyconversion process by the interaction of multiple radiation sources. This paper alsostudies on the constructive interference of nonlinear Cherenkov radiation of domainwall arrays under certain condition, and proposes the concept of nonlinearSmith-Purcell effect. In the anomalous-dispersive-like environment, lots of newphase-matching configurations can be formed at the crystal interfaces, such asscattering light assisted conical second harmonic generation in bulk medium andlateral one-dimensional superlattice materials; and reflection phase matching at thecrystal surface.Taking advantage of enhanced nonlinear response at domain walls, nonlinearCherenkov radiation can be used in ultrashort pulse characterization technique, suchas autocorrelation measurement and frequency resolved optical gating (FROG). Thismechanism overcomes contradictions between phase-matched bandwidth and theconversion efficiency, and possesses lots of advantages such as simplicity, accuracy,and high-resolution. The enhancement of the nonlinear response also can be used forreal-time, non-destructive, and high resolution detection of domain wall, and3-Dreconstruction of domain structures.