  Since its first demonstration in 2016, the multi-pass spectral broadening
technique has covered impressive ranges of pulse energy (3 $\mu$J - 100 mJ) and
peak power (4 MW - 100 GW). Energy scaling of this technique into the
joule-level is currently limited by phenomena such as optical damage, gas
ionization and spatio-spectral beam inhomogeneity. These limitations can be
overcome by the novel multi-pass convex-concave arrangement, which exhibits
crucial properties such as large mode size and compactness. In a
proof-of-principle experiment, 260 fs, 15 $\mu$J and 200 $\mu$J pulses are
broadened and subsequently compressed to approximately 50 fs with 90 %
efficiency and excellent spatio-spectral homogeneity across the beam profile.
