Population Transfer Of Diatomic Molecules With Femtosecond Laser Pulses

Population transfer between different bound states has been the important research topic in the field of the ultrafast optics. It is widely applied in the fields of quantum computing, atomic and molecular collision dynamics, molecular spectroscopy and light control chemical reactions. It is a focus of research that how to realize efficient population transfer. In this paper, the one dimensional time-dependent wave packet method is used to solve the time-dependent Schrodinger equation. The initial wave packet is obtained by utilizing the Fourier Grid Hamiltonian (FGH) method. The wave packet evolution with time can be solved by applying the split operator and the fast Fourier transformation (FFT).In the study of population transfer, we employ the Stimulated Raman Adiabatic Passage (STIRAP) and investigate the population transfer between electronic states of the NaH molecule driven by two femtosecond laser pulses. The wave packets of the three states are analyzed. The results show that the population can achieve efficient transfer via STIRAP.We study the effect of laser intensity on the population transfer. Large population transfer is observed with the increase of the pump and Stokes intensity, especially when the intensity of the pump and Stokes is matched. When the laser intensities are 5.0×1012 W/cm2, more than 95% population is transferred to the target state. When the laser intensities increase to 8.0 X 1012 W/cm2, the efficiency of the population transfer can be closer 100%.The population transfer also depends on the delay between the pump and Stokes laser pulse. The population transfer with delay times are discussed in detail. The results show that the population can be transferred effectively when two counterintuitive and partially overlapping pulses are used.The detunings of pulses influence on the population transfer. An efficient population transfer can be realized under the resonant or two-photon resonant condition.The population can be transferred to different states when the chirped pulses are used. When the chirped rate ?=-2,98.5% population transferred to the A1?+ state from the X1?+ state. All population can be transferred to the B1? state when the chirped rate ?= 22.