Femtosecond Nonlinear Optical Dynamics Of Organic Molecule Including Benzene

Femtosecond laser pulse is widely applied to research on the properties of nonlinear optical materials of all kinds due to its high peak intensity, ultrashort duration and extremely high momentary power. The organic nonlinear optical materials have a good many characteristics, for example, easy to synthesize, good mechanical property, big optical nonlinearity, high laser damage threshold, ultrafast response time and so on. Thus the organic nonlinear optical materials are extensively used in many field such as optical fiber communications, optical computing, light holography, medical laser, laser beam weapons, making them become one of the centers in functional materials currently. The research on the nonlinear dynamic of organic optical materials could strengthen our cognition about the relationship between the structure and the performance, thus providing theoretical support for the integration of photonic devices.The thesis studied the interaction between femtosecond laser pulse and the organic molecular system by adopting time-resolved optical Kerr effect technique, and then discussed the nonlinear dynamic properties of four kinds of organic molecules—benzene, o-xylene, toluene and nitrobenzene under the action of femtosecond laser pulse.The thesis firstly analyzed the femtosecond nonlinear response mechanism by the Dedye relaxation model under the incentive of femtosecond pulse, including the electronic transient response, the intermolecular motion and the intramolecular motion. The thesis also discussed the influence of distinctive response mechanism on time-resolved optical Kerr effect theoretical curve and that of different parameters on the time-resolved optical Kerr effect signals. Based on the theoretical analysis, by utilizing time-resolved optical Kerr effect, the experiment studied the third-order nonlinear dynamic process of the pure liquid benzene, o-xylene, toluene and nitrobenzene under the laser pulse at the wavelength of 800 nm, the pulse duration of 130 fs, and found that al the organic liquids include four style nonlinear dynamic processes: electronic transient response, molecular vibration, molecular reorientation and the interaction of induced dipole. The corresponding relaxation time of different response processes become longer with the order of benzene, toluene and nitrobenzene. The third-order nonlinear dynamic process of pure liquid benzene and o-xylene is similar. The paper analyzed the influence of the substitutional group on the benzene ring, liquid viscosity, the volume of molecule and molecular rotation to the nonlinear dynamic process for observing variation of relaxation time from the experiment. The orientation relaxation process of the four kinds organic reagents were described by Debye-Stokes-Einstein relation; utilizing the influence of substituent effect to theπelectron cloud density, the paper analyzed the relaxation process of the four kinds organic reagents; and analyzed the influence of symmetry of molecular rotation on the relaxation process by calculating the moment of inertia of samples along the different shaft.