  Recent results demonstrating the chaotic behavior of geodesics in
non-homogeneous vacuum pp-wave solutions are generalized. Here we concentrate
on motion in non-homogeneous sandwich pp-waves and show that chaos smears as
the duration of these gravitational waves is reduced. As the number of radial
bounces of any geodesic decreases, the outcome channels to infinity become
fuzzy, and thus the fractal structure of the initial conditions characterizing
chaos is cut at lower and lower levels. In the limit of impulsive waves, the
motion is fully non-chaotic. This is proved by presenting the geodesics in a
simple explicit form which permits a physical interpretation, and demonstrates
the focusing effect. It is shown that a circle of test particles is deformed by
the impulse into a family of closed hypotrochoidal curves in the transversal
plane. These are deformed in the longitudinal direction in such a way that a
specific closed caustic surface is formed.
