The onset of an electron parametric instability and 3/2 harmonic generation in variable-scale-length plasmas on solid surfaces using femtosecond pulses is observed. With the intensity approaching 10(18) W/cm(2), the instability threshold is already reached at plasma scale lengths of the order of the laser wavelength. A well-collimated harmonic emission with unusually broad spectrum is obtained.

We describe a nonlinear optical system that supports spiral pattern solutions in the field intensity. This new spatial structure is found to bifurcate above a secondary instability in the internally pumped optical parametric oscillator. The analytical predictions of threshold and spatial scale for the instability are supplemented by detailed numerical investigations of the formation of spiral p...

We show that one-dimensional parametric spatial solitons undergo temporal instability that leads to their breakup into spatiotemporal patterns with a characteristic snakelike shape.

The two-dimensional stability of vertically sheared inertial oscillations at ocean fronts is explored through a linear analysis and nonlinear simulations. Baroclinic effects reduce the minimum frequency inertia-gravity waves to an extent determined by balanced Richardson number ${{Ri}}$ front. Below critical value , which depends on strength shear, become unstable parametric subharmonic instabi...

Eigenmode coalescence imparts remarkable properties to non-hermitian time evolution, culminating in a purely spectral degeneracy known as an exceptional point (EP). Here, we revisit evolution at the EP and classify two-level Hamiltonians terms of M\"obius group. We then leverage that classification study dynamical encircling, by applying it periodically-modulated (Floquet) Hamiltonians. This re...