MULTIPHOTON ELECTRONIC COHERENCES WITH PULSE-SHAPE SPECTROSCOPY

We investigate multiphoton electronic coherences in a series of molecules with increasing complexity in non-adiabatic couplings driven by pairs of few-cycle, phase-locked deep-ultraviolet pulses with independent control of the relative phase and time delay. By combining measurements of the ionization yield with selected relative phase differences between the pulses, we can pick out different multiphoton orders and enable control over and measurement of specific pairs of electronic states. We contrast electronic coherences between states separated by two-photons (9.5eV), one-photon (4.75eV) and within our laser bandwidth (<0.2eV), resulting in electron-density modulations with periods ranging from 430 attoseconds to several femtoseconds. These fast electronic dynamics are tracked simultaneously with the accompanying nuclear motion. In addition, we derive analytic expressions for the measured ionization yield as a function of pump–probe delay and demonstrate their use as a quantitative tool for isolating individual photon-order contributions within the total yield.