Tracking attosecond electronic coherences using phase-manipulated extreme ultraviolet pulses

The extension of coherent time-resolved spectroscopy to extreme ultraviolet (XUV) photon energies is highly desirable as it offers unprecedented site-specificity by accessing localized inner-shell states and opens the door to attosecond time resolution. However, these experiments are extremely challenging due to the required ultra-high phase stability and the lack of phase-matching/cycling schemes necessary to isolate subtle coherence signals. For these reasons, a real-time study of the evolution of an XUV electronic coherence has not been reported and only few examples of quantum beat and vibrational wave packet (WP) studies have been demonstrated so far. In the present work, we implement a phase modulation technique for XUV pulse sequences, which facilitates both flexible coherent control schemes, and advanced coherent nonlinear spectroscopy techniques.