The Study Of Atomic Electron Dynamics Using Femtosecond Laser Pulse

Femtosecond pump-probe technology is widely used to investigate ultrafast phenomenon and the time resolution in femtosecond is realized by tuning the delay between pump and probe pulses.In traditional pump-probe measurement,the weak probe pulse will detect and perturb the quantum system excited by pump pulse.This dynamical process can be well understood by third-order perturbation theory.The medium-strength-field is known as the transition area between strong-field and weak-field regimes,and the perturbation theory has already broken down but ionization or dissociation can still be ignored in this regime.Due to the high nonlinearity of light-matter interaction,it is difficult to understand the ultrafast dynamics evolution of the aimed system.The atomic and molecular in the medium-strength-field was rarely studied.Here,a novel approach is developed to understand the ultrafast dynamics of an atomic system in medium-strength-field regime.The nonlinear effect induced by the medium-strength laser pulses are considered as a modification of third-order perturbation theory,inheriting the valuable characteristics of perturbation theory.The transitions from the ground state 5s ²S_1/2 to excited states 5p ²P_1/2,3/2 are far strong than other transitions in rubidium,and a well isolated V-type three-level system is formed.Experimental measurement in which changeable probe-pulse and pump-pulse intensity are used is performed in this multilevel system.The coincidence between experimental data and the analytical model indicates that the analytical model is effective.