  The breakup of high-order spatial solitons propagating in an AlGaAs slab
waveguide is studied. We experimentally observe the breakup of such beams into
multiple fragments and identify the mechanism of this breakup as the combined
effect of two- and three-photon-absorption. We show that the multiple breakup
persists even when the value of two-photon-absorption is reduced by an order of
magnitude owing to the high value of three-photon-absorption of AlGaAs at the
half band-gap. The experimental results extend known mechanism of soliton
breakup induced by two-photon-absorption and agree well with numerical beam
propagation simulations.
