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High harmonic generation in SF 6 : Raman-excited vibrational quantum beats

2007; IOP Publishing; Volume: 40; Issue: 18 Linguagem: Inglês

10.1088/0953-4075/40/18/f01

1361-6455

Zachary B. Walters, Stefano Tonzani, Chris H. Greene,

Advanced Chemical Physics Studies

In a recent experiment (Wagner et al 2006 Proc. Natl Acad. Sci. USA 103 13279) on SF6, a high-harmonic generating laser pulse is preceded by a pump pulse which stimulates Raman-active modes in the molecule. Varying the time delay between the two pulses modulates high harmonic intensity, with frequencies equal to the vibration frequencies of the Raman-active modes. We propose an explanation of this modulation as a quantum interference between competing pathways that occurs via adjacent vibrational states of the molecule. The Raman and high harmonic processes act as beamsplitters, producing vibrational quantum beats among the Raman-active vibrational modes that are excited by the first pulse. We present an improved version of the widely used three-step model, which tracks the evolution of the molecule's vibrational state and employs a rigorous treatment of the complicated electron–molecule recombination.