  A novel optical layout for a multi-pass resonator is presented paving the way
for pulse energy scaling of mode-locked thin-disk lasers. The multi-pass
resonator we are proposing consists of a concatenation of nearly identical
optical segments. Each segment corresponds to a round-trip in an optically
stable cavity containing an active medium exhibiting soft aperture effects.
This scheme is apt for energy and power scaling because the stability region of
this multi-pass resonator contrarily to the 4f-based schemes does not shrink
with the number of passes. Simulation of the eigen-mode of this multi-segment
resonator requires considering aperture effects. This has been achieved by
implementing effective Gaussian apertures into the ABCD-matrix formalism as
lenses with imaginary focal length. We conclude proposing a simple way to
double the stability region of the state-of-the-art layouts used in industry
achievable by a minimal rearrangement of the used optical components.
