Rotational branching in population transfer in H2 by chirped adiabatic Raman passage

Abstract

We have theoretically investigated the branching in population transfer in H2 by chirped adiabatic Raman passage from the ground vg=0, Jg=0 level to the final rotational levels Jf=0 (Q-branch) and Jf=2 (S-branch) of the fundamental transition (vf=1) in the ground X 1Σg+ state via the nonresonant intermediate B 1Σu+ and C 1Πu+ states. The density matrix technique has been employed to describe the time evolution of the process. We have evaluated the rotational branching of transferred population in the final levels using linearly chirped pump and Stokes laser pulses with different chirp rates and chirp widths. Both the pulses are considered to have the same temporal shape, duration, peak intensity, and linear parallel polarizations. It has been observed that for negative chirping of the pump laser and positive chirping of the Stokes laser, branching in population transfer to the Q- and S-branches occur for fast chirping and short pulses while for slow chirping and long pulses, more and more population builds up in the S-branch. When the chirpings of the pulses are reversed, total population is transferred only to the Q-branch. We have endeavored to interpret the results within the framework of the adiabatic energy eigenvalue picture and the relative values of the two-photon Raman matrix elements for the two transitions.