1. An optical arrangement for enlarging spectral bandwidths by nonlinear self-phase modulation for shortening ultrashort pulses, wherein a multipass cell and a nonlinear medium are used, wherein the nonlinear medium is arranged within the multipass cell, and a laser beam having ultrashort pulses passes through the nonlinear medium multiple times, wherein the laser beam is coupled into the multipass cell by way of a shaping optical unit, wherein the laser beam is shaped into an astigmatic beam and coupled into the multipass cell by way of the shaping optical unit.
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