The effect of volumetric weighting in the interaction of intense laser fields with clusters

Silver clusters embedded in helium nanodroplets are exposed to intense femtosecond laser pulses (1013 - 1016 W/cm2). The signal of highly charged (q≤11) atomic fragments is maximized by delayed plasmon enhanced ionization using stretched laser pulses. Further details with respect to the dynamics of the charging process can be obtained, when the intensity distribution within the laser focus is taken into account. For the first time, the z-scan method is applied to clusters which offers a route to investigate the explicit dependence of the ion signals with respect to the laser intensity. By taking advantage of the volumetric weighting effect ionization thresholds are determined, yielding values well below 1014 W/cm2 for Agq+ ions with q≤11