Observation of field phase dependent autoionization

We report on the observation of a field phase dependent autoionization rate of calcium in the region of the doubly excited state. Excitation of the autoionizing state occurs from the atomic ground state through two phase related and hence interfering channels, namely a three photon channel and a single photon channel , being the third harmonic of . The autoionization rate exhibits a sinusoidal modulation as a function of the relative phase of the two excitation fields. Both ionizing fields are not focused in the interaction region, thus demonstrating the possibility of phase control in a large interaction volume and free of phase shift effects associated with focused geometries.