  We experimentally demonstrate simultaneous spatial and temporal compression
in the propagation of light pulses in multimode nonlinear optical fibers. We
reveal that the spatial beam self-cleaning recently discovered in graded-index
multimode fibers is accompanied by significant temporal reshaping and up to
four-fold shortening of the injected sub-nanosecond laser pulses. Since the
nonlinear coupling among the modes strongly depends on the instantaneous power,
we explore the entire range of the nonlinear dynamics with a single optical
pulse, where the optical power is continuously varied across the pulse profile.
