Extreme-ultraviolet Ramsey-type spectroscopy

We performed an experimental and theoretical investigation of Ramsey-type spectroscopy in conjunction with high-order-harmonic generation. The ninth harmonic (lambda similar or equal to 88 nm) of a femtosecond Ti:sapphire laser was used to excite a pair of autoionizing states of krypton. The outcome of the ionization process, detected by an ion-mass spectrometer, shows the characteristic quantum interference pattern. The behavior of the fringe contrast was interpreted on the basis of a simple analytical model, which reproduced well the experimental results without any free parameter.