Atomic And Molecular Dynamic In Strong Laser Field

With the development of laser technology,strong laser pulse within fem-tosecond or even attosecond duration could interact with atom and molecule,which will induce interesting nonlinear effects.Based on these phenomena atomic and molecular dynamics can be detected in femtosecond timescale.The first work of this thesis is the theoretical investigation on high-order harmonic generation in a two-color multi-cycle inhomogeneous field combined with a 27th harmonic pulse.By considering a bowtie-shaped gold nanostruc-ture,the spatiotemporal profiles of enhanced plasmonic fields are obtained by numerically solving the Maxwell equation using finite-domain time-difference method.Based on quantum-mechanical and classical models,the effect of 27th harmonic pulse,temporal profile of enhanced plasmonic field and inhomogene-ity on supercontinuum generation are analyzed and discussed.As a result,broadband supercontinuum can be generated from our approach with optimized gap size of nanostructure.Moreover,these results are not sensitively dependent on the relative phase in the two-color field.In the second work in this thesis,we examine the residual current to in-vestigate the conversion efficiency from the few-cycle laser pulse into the tera-hertz radiation of H₂⁺by solving the time-dependent Schr¨odinger equation in the non-Born-Oppenheimer approach.It is found that the nuclear motion and high vibrational states will improve the optical-to-terahertz conversion efficiency sig-nificantly,while with the increasing of the laser intensity,ionization saturation will suppress the effects of moving nuclei.Moreover,based on the dependence of the residual current on the delay time of the nuclear vibration,we conclude that the terahertz signal may serve as a tool to probe the nuclear dynamics.The third work of this thesis talks about electron localization in H₂⁺.The wavelength dependence of electron localization of H₂⁺and its isotopomers in the ultraviolet pump-probe scheme is investigated by numerically solving the time-dependent Schr¨odinger equation.By combining with a semiclassical method,an effective analytical formula expressed in the adiabatic representation is es-tablished to describe the localization probability with several zero crossings.A stable zone with respect to the laser intensity and carrier envelope phase is found at a relatively long probe wavelength.Slower nuclear motion of heavier isotopomers leads to a longer critical wavelength.The last work of this thesis is that we reexamine the recent pump-probe experiment with O₂using short intense infrared laser pulses theoretically.Us-ing parameters that closely mimic the experimental conditions and taking into account the angle-dependent population redistribution due to resonant coupling between the relevant states,we show that the observed kinetic energy release spectra,including the energy-dependent structure and the quantum beat fre-quencies,can be accurately reproduced.Our results reveal additional impor-tant channels that were missed earlier.In particular,the strong contributions from O₂⁺a⁴?_uand b⁴?_g⁺states lead to the possibility of observing the inter-channel beating.We further demonstrate that,by varying the laser parameters,the coherent nuclear wave-packet motions on different potential energy surfaces?PESs?can be probed and the properties of the PES can be examined.Future experiments with different wavelength lasers are proposed for better probing and controlling nuclear dynamics on different PESs.