  Quantum calculations of tunneling in strong-field ionization (SFI) predict
intricate momentum distributions due to sub-laser-cycle attosecond electron
dynamics. These are obscured in most experiments by the dominance of
inter-cycle interference patterns which are the hallmark of above-threshold
ionization (ATI). Highly controlled 1- to 2-cycle laser pulses produce less
inter-cycle interference but cannot accurately recreate the sub-cycle 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 sub-cycle features in experimental multi-cycle 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 sub-cycle
interference structures in unprecedented detail. We can resolve new modulations
in holographic structures that have not been previously noted in earlier
experiments and which provide a new reference for comparing to calculations.
