Two-Photon Fluorescence Property and Ultrafast Dynamics of Two Dipolar Compounds with Dipicolinate as Electron Acceptor

Linear and nonlinear photophysical properties of two novel dipolar compounds named as trans- dimethyl-4-[4＇-（N,N-dimethylamino）-styry1]-pyridin-2,6-dicarboxylate （Xiao-1） and trans-dimethyl-4-[4＇-（N,N-diphenylamino）-styry1]-pyridin-2,6-dicarboxylate （Xiao-2） are investigated by steady-state absorption and fluorescence spectroscopy, Z-scan and two-photon excited fluorescence measurements. Strong two-photon fluorescence emission and the pronounced positive solvatochromism are observed from two compounds. The two-photon absorption cross section of Xiao-2 is about 1.5 times larger than that of Xiao-1. One-color and two-color femtosecond pump-probe experiments are employed to investigate the excited state dynamics of two compounds. The relaxation lifetime of the intra-molecular charge transfer state is determined to be in the hundreds of picosecond domain for both the compounds in THF, and several tens of picosecond in DMSO solutions.     

Nonlinear Optical Properties and Ultrafast Dynamics of Undoped and Doped Bulk SiC

Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the wavelength of 800hm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.