Theoretical Study On Two-dimensional Second-order Nonlinear Optical Property Of Electron-push-pull Nano-molecule

In recent years,the characterization of second-order nonlinear optical propertyχ^（2）is mainly focused on static first hyperpolarizability and the single process of SHG（second harmonic generation）,SFG（sum frequency generation）,DFG（difference frequency generation）and so on.The study of two-dimensional nonlinear spectra is mainly in the two-dimensional electronic spectra of generate four wave mixing in third nonlinear optics and multi-dimensional nonlinear optical spectra.Two-dimensional second order nonlinear optical spectra containing all the second-order nonlinear optical response information was obtained by scanning in continuously varying frequency,which help us understand the second-order nonlinear optical information.Obtaining a laser source with continuously varying frequency is difficult in experiment.With this limitation,it is not an easy task to obtain experimentally two-dimensional nonlinear optical spectra and this feasible with theoretical calculation with much higher efficiency and less resources.In chapter 3,based on the D-π-A with excellent nonlinear optical performance,the studies on the second-order response process,charge distribution,contribution of two-level and three-level model,orbital transition and so on,are carried out.The relation between molecular structure and nonlinear optical property is disclosed,and a good method was proposed to improve the first hyperploarizability.In chapter 4,an enhancement of almost 5,000 times in the second-order NLO response compared with the response of individual molecules has been reported in DANS@oSWCNT（head-to-tail order in opened single wall carbon nanotube）.However,only the dipolar molecules with head-to-tail in one-dimensional confinement cannot reach so giant second-order nonlinear optical response.The studies on the second-order response process,charge distribution,contribution of two-level and three-level model are performed,electron transition was used to reveal the role of nanotube in DANS@oSWCNT.The nanotube is polarized,and the electrons of nanotube with dipolar molecules re-distributed,and lead to the long distance charge transfer.So the interaction between DANS and SWCNT,especially the polarization of nanotube by dipolar molecules,contributes significantly to the second-order nonlinear optical response of DANS@oSWCNT.