Ionization dynamics in two-color laser fields - "phase-of-the-phase" spectroscopy and semi-classical trajectory analysis

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Understanding strong-field ionization dynamics provides the basis for structural and dynamical imaging of matter, acceleration of particles, and novel radiation sources using intense laser pulses. Compared to "standard" momentum-resolved photoelectron spectra, the recently introduced "Phase-of-the-Phase" (PoP) spectroscopy gives additional information about the target-specific strong-field ionization dynamics. The idea is to record the change in the yield and its phase lag with respect to the relative phase of a two-color pulse, providing an enhanced sensitivity on a subcycle timescale and eliminating thermal or other incoherent electron emission processes that otherwise clutter strong-field photoelectron spectra from multi-electron systems. We propose to investigate in a joint experimental and theoretical effort the dependencies of PoP spectra on target properties and laser wavelength. Atomic targets (hydrogen, alkalies, rare gases) as well as finite systems (SF6, C60) will be studied in order to systematically investigate the prospects of PoP as regards, e.g., (dynamical) self-imaging, for increasing target complexity. Since PoP spectroscopy can be easily extended towards longer wavelengths, measurements on low-ionization-potential targets can be performed within the semi-classical regime. The powerful theoretical tool of quantum trajectories is then applicable, yielding unprecedented and intuitive insight into the underlying physical mechanisms.