Spatiotemporal light-beam compression from nonlinear mode coupling

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 fourfold shortening
of the injected subnanosecond 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.