Research On Second-harmonic Generation And Two-photon Absorption Properties Of One/two-dimensional Semiconductor Nanostructures

As one of the major subfield of modern optics,nonlinear optics has lay a great foundation for studying light-matter interaction and developing practical sciences and technologies.Recently,with the development of nanomaterials and nanotechnologies,the study on nonlinear optical properties of semiconductor nanomaterias has become a new research field.This field is of great importance for deeply understanding light-matter interaction at micro/nanoscale,controlling the nonlinear optical field and developing optical nanodevices.Second harmonic generation(SHG)and two-photon absorption(TPA)are two of the most fundamental and commonly used nonlinear optical effects.Because of their relatively simple processes and high efficiencies,it is most likely to make the optical nanodevices into practice with these two effects.Focusing on the SHG/TPA properties of several one/two-dimensional semiconductor nanomaterials and nanostructures,the main contents and the innovations of our work are as follows:(1)We study the surface second harmonic generation(SSHG)properties in a single Zinc Telluride(ZnTe)nanowire.Different from the bulk SHG in the noncentrosymmetric structures,SSHG originates from the broken of centrosymmetry or centrosymmetic inversion at the surface/interface.Because of that,SSHG is usually produced from the atomatic layers at the material surface.In the experiment,we have observed the laterally emitted SSHG in a single ZnTe nanowire for the first time.We perform systematic investigations on the directionality,conversion efficiency and anisotropic property of the SSHG We find that the SSHG has a low divergence angle of 4° and a high conversion efficiency of?10-6.Furthermore,the anisotropic property of the SSHG is found to be strongly dependent on the crystalline of the ZnTe nanowire.The results suggest that the SHG in single nanowires is of great potential for applications in high-quality coherent nanosources and nonlinear optical detection of nanostructures.(2)We study the resonance enhanced SHG in c-axis oriented Zinc Oxide(ZnO)nanorods.With theoretical derivation and experimental verification,we find that the SHG collected in the c-axis oriented ZnO nanorods is dominantly by the ?xaz component of second-order nonlinear susceptibility.Based on that,the resonance enhanced SHG property is studied in the the c-axis oriented ZnO nanorods.And then,the value of ?xaz under resonance is measured to be about 20.2 pm/V,which is much larger than those of the commonly used beta-barium borate(BBO)and potassium dihydrogen phosphate(KDP)crystals.This indicates that there is a strong second-order nonlinear effect in the c-axis oriented ZnO nanorods on resonance.Furthermore,by performing numerical simulations with finite-difference time-domain(FDTD)method,it is found that the local-field effect in the c-axis oriented ZnO nanorods have also contributed to the enhanced second-order nonlinear susceptibility.The result indicates that the SHG intensity has been enhanced by 4 folds with the local-field effect.This study provides a new method to further enhance the SHG efficiency,and lays great foundation for achieving high-efficiency coherent nanosources.(3)We study the TPA properties of the flakes of 2D perovskite phenylethylamine lead iodide((PEA)2Pbl4).Different from the corner sharing framework of 3D perovskites,2D organic-inorganic perovskites possess a layered staking structure composed of alternative organic and inorganic components,which is silimilar to the multi-quantum-well structure.With static intensity dependent measurement,the TPA coefficient of a(PEA)2Pbl4 flake is determined to be about 211.5 cm/MW at 800 nm,which is at least one order of magnitude larger than those of 3D perovskite films and some typical semiconductor nanostructures.The giant TPA can be attributed to the enhanced quantum and dielectric confinement in the organic-inorganic multi-quantum-well structure.In addition,the experimental results suggest a highly thickness-dependent TPA and an excellent stability for the 2D perovskite flakes.The result advocates a great promise of 2D organic-inorganic perovskites for nonlinear optical absorption related optical devices.