A. Aumann et al., Magnetic field control over microscopic symmetry properties of an optical pattern-forming system: experiment, J OPT B-QUA, 2(3), 2000, pp. 421-425
We study the selection between hexagonal and square polarization patterns i
n a sodium vapour cell with optical feedback provided by a single mirror. S
canning an external magnetic field, a transition sequence from squares via
negative hexagons, squares, and positive hexagons again to squares is obser
ved close to the instability onset. Well above threshold the hexagons give
way to squares in a secondary bifurcation. These observations demonstrate h
ow the macroscopic symmetries of optical patterns can be controlled by mani
pulating the microscopic symmetries of the light-matter interaction. The ke
y to this control is the vectorial degrees of freedom of the optical patter
n-forming system.