Femtosecond space–time coupling effects in dispersive nonlinear media are investigated by a simple approximate method. The applicability of the method is verified by comparison with earlier numerical simulations. New results are presented for astigmatic beams as well as for negative dispersion. The position of the beam waist in the material changes the collapse threshold. For astigmatic beams, collapse is prevented for pulse durations shorter than a critical value.
© 1996 Optical Society of America
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