Influence of space-time focusing on spatiotemporal instability in dispersive self-focusing media is investigated on the basis of a modified nonlinear Schrodinger equation (NLSE) beyond the slowly varying envelope approximation. It is found that, for both normal and anomalous dispersions, space-time focusing may lead to the appearance of new instability regions. Space-time focusing influences the original spectra obtained using the standard NLSE mainly by shrinking the insta...
