Photorefractive Solitons (Chapter in Springer book ... - Tripod

30 E. DelRe, M. Segev, D. Christodoulides, B. Crosignani, and G. Salamo
to soliton physics: not only energy (power) and momentum are conserved,
but also the conservation of angular momentum, which is the fundamental
symmetry that enables spiraling. These pioneering experiments are a characteristic
example of the contribution of photorefractive solitons to nonlinear
science.
Fig. 20. Collisions, from [49]. Top view of colliding incoherent diffracting beams
and solitons for different relative angles.
Fig. 21. Hybrid-soliton collisions, from [104]. (a) input launch of a two-dimensional
and a one-dimensional diffracting beam, output intensity distribution with no applied
field, output intensity distribution with applied self-trapping field; (b) same
as (a) but for a smaller collision angle; (c-d) single beam self-trapping in the same
experimental conditions.
It is interesting to compare soliton and plane-wave interaction phenomenology
in a photorefractive. The crossing of two plane waves, even at low
angles of the order of fractions of a degree, leads to energy transfer, which,
even if mediated by space-charge components of the order of η, brings to
finite if not total coupling from one beam to the other. Two solitons, on the
other hand, behave in a diametrically opposite manner: they cross each other
without appreciable energy transfer, even when they are mutually coherent.