Controlling Electron Dynamics And Material Properties By Ultrafast Laser

Femtosecond laser(151fs 10 s-?) has properties of short pulse duration, high intensity and large energy, therefore it can be used to fabricate various materials with high precision,fast speed, and small thermally affected zone. Moreover,attosecond laser(181as 10 s-?),with a duration shorter than femtosecond laser, can be applied to control electron dynamics directly within electronic relaxation time. When the field intensity reaches12 210 W/cm,nonlinear absorption mechanism dominates the electron excitation process, in which electrons are excited through multiphoton ionization, tunneling ionization and avalanche ionization. Therefore, it is available to control the electron dynamics by adjusting the power density of the optical field.Ultrafast intense laser fabrication is a nonlinear multi-scale process, from femtosecond to microsecond, and from nanometer to micrometer. Therefore, different theoretical tools are applied to describe laser-material interactions in different time domains. Moreover,quantum mechanics is involved in the photon absorption process within femtoseconds. Due to its advantages of high calculation accuracy and short calculation time, time-dependent density functional theory(TDDFT) has become the only effective method to investigate the nonlinear electron dynamics in multiple electron systems.In this paper, electron dynamic controlling by ultrafast laser is investigated within the framework of TDDFT. The main work includes:(1) Controlling electron dynamics by elliptically polarized femtosecond laserThe ionization mechanics and electron density distribution of Al in elliptically polarized femtosecond laser is investigated. Three main factors which influence electron ionization rates are proposed. Moreover, their effects are evaluated and compared.(2) Using femtosecond and attosecond lasers to control the conductivity of dielectricThe mechanism of controlling dielectrics’ electric properties by compound influence of attosecond and femtosecond lasers is investigated. The diamond’s conductivity is enhanced obviously within several attoseconds. The response frequency of diamond in experiment is improved by three orders.(3) Controlling the breakdown process of dielectric by two femtosecond lasersWhen affected by two femtosecond lasers, the electron dynamics in diamond in the process into breakdown is investigated with regard to polarization and polarized currents.Two new criterions are proposed in order to test whether breakdown happens.