  The generation of terawatt (TW) near-single-cycle laser pulses is of high
interest for applications including attosecond science. Here we demonstrate a
three-stage post-compression scheme in a non-guided geometry using He as the
nonlinear medium, resulting in the generation of multi-mJ pulses with a
duration of 3.7 fs. Key features of this approach are its simplicity,
robustness and high stability, making it ideally suited for highly demanding
applications such as attosecond-pump attosecond-probe spectroscopy (APAPS).
This is demonstrated by performing two-color APAPS in Ar and Ne, where both
simultaneous and sequential two-photon absorption are observed. Our approach is
scalable to multi-TW powers.
