Optical Nonlinearity And Optical Limiting Of Polycyclic Aromatic Organic Small Molecules

The development of the discipline of nonlinear optics is inseparable from the synthesis and discovery of nonlinear optical materials.Therefore,exploring the properties of certain nonlinear optical materials and designing the molecular structure of excellent organic nonlinear optical materials have become the focus of increasing attention.Because of its good nonlinear properties,PAHs are a class of organic optical nonlinear materials of relatively high quality.They also have good fluorescence properties and strong push-pull electron capabilities,and therefore have excellent application prospects in the fields of display,dye probes,and optical limiting.In this dissertation,two kinds of organic polycyclic aromatic hydrocarbons with similar molecular structures were studied.Firstly,two materials were linearly characterized to obtain ultraviolet-visible absorption spectra and fluorescence emission spectra.Afterwards,the quantum molecular chemical theory was used to calculate the front molecular orbital distribution and energy level band gap.Next,two kinds of materials were separately subjected to Z-scan experiments with nanosecond and picosecond pulse widths and different energies to investigate the third-order nonlinear response of the two materials.Both of the two molecular solutions showed significant reverse saturation absorption and were obtained.The nonlinear physical mechanism of the Z-20 material is caused by the interaction of the two-photon absorption third-order effect and the two-photon absorption-induced absorption of the excited state.The Z-33 material is a third-order nonlinear absorption mechanism caused by purely excited state absorption,and the corresponding effective nonlinear absorption coefficient is fitted.Finally,through the picosecond pump detection technology and femtosecond transient absorption technology,the internal excited states of two kinds of material molecules and the transition laws of energy levels were studied.The energy level model and energy level rate equation of the two molecules were determined and we fitted relevant parameters such as absorption cross section and energy level lifetime.It is analyzed that the molecules with electronic push-pull structure have stronger nonlinear properties than ?-?* transitions,and the possibility of applying Z-20 materials in the field of optical limiting is explored.