Hexagons, flowers and dynamical phenomena in a quasi-scalar situation
With circular input situation the light-matter interaction is quasi-scalar.
This case is in some sense closest to the original proposal (D'Alessandro),
but the results go far beyond since the nonlinearity in the atomic vapor
is more complex and creates a richer phenomenology. We observe a transition
between negative and positive hexagons as well as flowers which are created
by saturation in beam center.
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Typical patterns observed in the near field intensity distribution
of the transmitted beam for increasing input power.
Top row: simulations,
bottom row: experiment. See Ackemann
1995 for details. |
The positive hexagons are unstable versus their own harmonics due to
a near coincidence with another instability balloon. Since the smallest
harmonic wavenumber is sqrt(3) for hexagons in two spatial dimensions (and
not two as in temporal systems), the resulting 'ultrahexagons' have a length
scale which is a factor of sqrt(3) smaller than the linear prediction.
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Fundamental wavevectors creating the primary hexagonal lattice (blue)
and their 'harmonics' (green) |
 List of publications
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