Spatiotemporal soliton propagation in saturating nonlinear optical media

The simultaneous balance of nonlinear spatial self-focusing with diffraction and the compensation of dispersion with nonlinear temporal self-focusing, in a saturating nonlinear medium, give stable spatiotemporal solitons, or ``light bullets.'' An analytical approach for arbitrary saturating nonlinearity is established in order to investigate the dynamics of such light bullets. This approach is applied to nonlinear materials with negative fourth-order optical index. The analytically predicted exceptional robustness of light bullets that can be generated in a large range of parameters is confirmed by numerical simulations.