  Post-compression methods for ultrafast laser pulses typically face
challenging limitations including saturation effects and temporal pulse
break-up when large compression factors and broad bandwidths are targeted. To
overcome these limitations, we exploit direct dispersion control in a
gas-filled multi-pass cell, enabling for the first time single-stage
post-compression of 150 fs pulses and up to 250 uJ pulse energy from an
Ytterbium (Yb) fiber laser down to sub-20 fs. Dispersion-engineered dielectric
cavity mirrors are used to achieve nonlinear spectral broadening dominated by
self-phase-modulation over large compression factors and bandwidths at 98%
throughput. Our method opens a route towards single-stage post-compression of
Yb lasers into the few-cycle regime.
