Temporal phase control of bound-bound and bound-free two-photon transitions in NO with two time-delayed cross-polarized pulses

Temporal phase control over the multi-photoionization of NO is investigated experimentally The coherent excitation of the molecular system is achieved by a sequence of two phase-related non-Fourier-transform-limited laser pul ses delivered by a nanosecond dye laser, The phase-locked pulses are produc ed by making use of an actively stabilized interferometer with a tunable pa thlength difference. As the coherence time of the laser is comparable with the inhomogenous dephasing time of the medium, the measurements are perform ed with temporally overlapped pulses. In order to avoid the modulation of t he ionic signal coming from optical interference, the linear polarizations of the two pulses are crossed. The quantum modulation of the signal versus the time delay between the two pulses is observed for the three following d istinct processes: (a) two-photon resonant four-photon ionization of the gr ound vibronic state; (b) two-photon absorption of the A-X transition follow ed by ionization; and (c) two-photon ionization of the electronically excit ed state A. As a result, temporal phase control over bound-bound and bound- free transitions is demonstrated. The efficiency of the control process is shown to be limited by the presence of uncoupled excitation channels inhere nt to the method employed. The advantage in using a sequence of cross-polar ized pulses for the controlling processes is discussed.