Generation of optical spatiotemporal solitons

We report the experimental formation of optical spatiotemporal solitons. Intense femtosecond-duration pulses experience a saturable self-focusing nonlinearity due to the cascading of quadratic nonlinear processes. Strong coupling of the interacting fundamental and harmonic waves produces solitons that overcome diffraction in one spatial dimension as well as group-velocity dispersion to reach constant beam size and pulse duration, both compressed with respect to the input values. Spatiotemporal solitons are observed both with nearly zero and with large group-velocity mismatch between fundamental and harmonic pulses. [S0031-9007(99)09288-1].