6 research outputs found
Few-cycle soliton propagation
Soliton propagation is usually described in the ``slowly varying envelope
approximation'' (SVEA) regime, which is not applicable for ultrashort pulses.
We present theoretical results and numerical simulations for both NLS and
parametric () ultrashort solitons in the ``generalised few-cycle
envelope approximation'' (GFEA) regime, demonstrating their altered
propagation.Comment: 4 pages, 4 figure
Modulational instability in nonlocal nonlinear Kerr media
We study modulational instability (MI) of plane waves in nonlocal nonlinear
Kerr media. For a focusing nonlinearity we show that, although the nonlocality
tends to suppress MI, it can never remove it completely, irrespectively of the
particular profile of the nonlocal response function. For a defocusing
nonlinearity the stability properties depend sensitively on the response
function profile: for a smooth profile (e.g., a Gaussian) plane waves are
always stable, but MI may occur for a rectangular response. We also find that
the reduced model for a weak nonlocality predicts MI in defocusing media for
arbitrary response profiles, as long as the intensity exceeds a certain
critical value. However, it appears that this regime of MI is beyond the
validity of the reduced model, if it is to represent the weakly nonlocal limit
of a general nonlocal nonlinearity, as in optics and the theory of
Bose-Einstein condensates.Comment: 8 pages, submitted to Phys. Rev.
Modulation Instability of Ultrashort Pulses in Quadratic Nonlinear Media beyond the Slowly Varying Envelope Approximation
We report a modulational instability (MI) analysis of a mathematical model
appropriate for ultrashort pulses in cascaded quadratic-cubic nonlinear media
beyond the so-called slowly varying envelope approximation. Theoretically
predicted MI properties are found to be in good agreement with numerical
simulation. The study shows the possibility of controlling the generation of MI
and formation of solitons in a cascaded quadratic-cubic media in the few cycle
regimes. We also find that stable propagation of soliton-like few-cycle pulses
in the medium is subject to the fulfilment of the modulation instability
criteria