Forcing Reaction-Diffusion media with light: nonlocal coupling and symmetry breaking of Turing patterns

The response of pattern forming systems to a external forcing provides
a powerful tool to investigate the inherently nonlinear mechanisms of
self-organization under non-equilibrium constraints. In this talk I
will report on theoretical and experimental investigations of new
effects introduced by external forcing in two different light-sensitive
reaction-diffusion media: the Belousov-Zhabotinsky and the Cdima
reactions.
In the Belousov-Zhabotinsky reaction I will show that the sensitivity
to light can be exploited to introduce nonlocal-coupling to a otherwise
only diffusive media. This nonlocal coupling can be used to induce new
types of instabilities such as Turing and wave (i.e. a Hopf instability
at a nonzero wavenumber) which are otherwise absent without external
forcing. Further theoretical analysis of these new instabilities has
been performed. In particular I will show that a set of coupled
amplitude equations derived for the wave instability case allow us to
explore the nature of this instability in detail.

In the case of the Cdima reaction I will present new experimental
results showing a new symmetry breaking phenomenon of a intrinsic
striped pattern. This symmetry breaking is induced by a travelling
wave forcing and can be interpreted within an amplitude equation-based
generic framework. These equations take the form of three coupled
complex Ginzburg-Landau equations and a allow us to do predictions for
a wide range of forced systems.