Disentangling the subcycle electron momentum spectrum in strong-field ionization

Abstract

Quantum calculations of tunneling in strong-field ionization predict intricate momentum distributions due to sub-laser-cycle attosecond electron dynamics. These are obscured in most experiments by the dominance of intercycle interference patterns, which are the hallmark of above-threshold ionization (ATI). Highly controlled one- to two-cycle laser pulses produce less intercycle interference but cannot accurately recreate the subcycle features produced by uniform-cycle calculations due to the effect of the carrier envelope of the pulse. We present a simple and effective technique to recover these subcycle features in experimental multicycle spectra. We time-filter the momentum distribution to highlight features originating from the interference of electron trajectory pairs with ionization times less than one field cycle apart. This method removes the ATI patterns and reveals subcycle interference structures in detail. We can resolve modulations in holographic structures that provide a reference for comparing with calculations.