PHASE AND AMPLITUDE CONTROL IN THE FORMATION AND DETECTION OF ROTATIONAL WAVE-PACKETS IN THE E(1)SIGMA(-2()(G) STATE OF LI)

Femtosecond laser pulse amplitude/phase masking techniques are employe d to control the formation and detection of rotational wave packets in the electronic E (1)Sigma(g)(+) state of lithium dimer. The wave pack ets are prepared by coherent excitation of rovibronic E (1)Sigma(g)(+) a ( VE,JE) states of Li-2 from a single intermediate state, A (1)Sigm a(u)(+) (nu(A) = 11, J(A) = 28), and probed by time-resolved photoioni zation. In the detection step, the wave packet is projected onto the X (2)Sigma(g)(+) state of Li-2(+). New resonance structure in the X (2) Sigma(u)(+) ionic state continuum is obtained by measuring the wave pa cket signal modulation amplitude as a function of the frequencies remo ved from the spectrally dispersed probe pulse by insertion of a wire m ask in a single-grating pulse shaper. A split glass phase mask inserte d into the pulse shaper is used to produce step function changes in th e spectral phase of the pulse. The phase relation among the wave packe t states is varied by changing the relative phases of spectral compone nts in the pump pulse and is monitored by measuring the changes in the phase of the rotational wave packet recurrences using an unmodified p robe pulse. By altering the relative phases among the wave packet comp onents, the spatial distribution of the initial wave packet probabilit y density is varied, resulting in phase-dependent ''alignment'' of the probability density in angular space. Phase changes in the signal rec urrences are also observed when a phase modified pulse is used in the wave packet detection step after wave packet preparation with an unmod ified pulse. The formation and detection of the wave packets is discus sed in terms of quantum interference between different excitation rout es. The relative phase factors encoded in a single optical pulse (pump dr probe) are transferred into the interference term of the measured signal through the molecule-photon interaction. (C) 1998 American Inst itute of Physics. [S0021-9606(98)00222-0].