Phase and Amplitude Control in the Formation and Detection of Rotational Wave Packets in the E1Σg+ State of Li2

Published

June 1, 1998

Author(s)

R Uberna, Mouhamad Khalil, R M. Williams, J M. Papanikolas, S R. Leone

Abstract

Femtosecond laser pulse amplitude/phase masking techniques are employed to control the formation and detection of rotational wave packets in the electronic E¹Σ_g⁺ state of lithium dimer. The wave packets are prepared by coherent excitation of rovibronic E¹Σ_g⁺(Ņ_E,J_E) states of Li₂ from a single intermediate state, A¹Σ_g⁺(Ņ_A=11,J_A=28), and probed by time-resolved photoionization. In the detection step, the wave packet is projected onto the X²¹Σ_g⁺state of Li₂⁺. New resonance structure in the X²¹Σ_g⁺ ionic state continum is obtatined by measuring the wave packet signal modulation amplitude as a function of the frequencies removed from the spectrally dispersed probe pulse by insertion of a wire mask in a single-grating pulse shaper. The slit glass phase mask inserted into the pulse shaper is used to produce step function changes in the spectral phase of the pulse. The phase relation among the wave packet states is varied by changing the relative step function spectral components in the pump pulse and is monitored by measuring the changes in the phase of the rotational wave packet recurrences using an unmodified probe pulse. By altering the relative phases among the changes in the phase of the rotational wave packet recurrences using an unmodified probe pulse. By altering the relative phases among the wave packet components, the spatial distribution of the wave packet probability density is varied. The phase-dependent alignment of the probability density in the selected regions of space is demonstrated. Phase changes in the signal recurrences are also observed when a phase modified pulse is used in the wave packet detection step after wave packet preparation with an unmodified pulse. The formation and detection of the wave packets is discussed in terms of quantum interference between excitation routes. The relative phase factors encoded in a single optical pulse (pump or probe) are transferred into the interference term of the measured signal through the molecule-photon interaction.

Citation

Journal of Chemical Physics

Volume

108

Issue

No. 22

Pub Type

Journals

Keywords

coherent control, frequency mask, phase control, pulse shaping, quantum interference, wave packet

Citation

Uberna, R. , Khalil, M. , Williams, R. , Papanikolas, J. and Leone, S. (1998), Phase and Amplitude Control in the Formation and Detection of Rotational Wave Packets in the E¹Σ_g⁺ State of Li₂, Journal of Chemical Physics (Accessed October 17, 2025)