Linear response in the strong-field domain: ultrafast wave packet interferometry in the continuum

We demonstrate that there are cases in which the response of a molecular system to the effects of a strong laser field is linear. By numerically solving the quantum dynamics of a wave packet of photo-dissociated H, we show that the initial state depletion and the photodissociation yields to various final channels may at times be an essentially linear function of the laser peak intensity. We have also investigated the case when the excitation is performed with delayed pulses, where the linear response regime is accompanied by oscillations in the population of vibrational and rotational states as a function of the delay time. In keeping with the observation of linear response beyond the weak field perturbative limit, coherent control over branching ratios, which can only exist in the strong field regime, is also shown to be extensive.