Jf. Scott et al., SELF-ASSEMBLY OF HEXATIC OPTICAL-PATTERNS IN FERROELECTRIC-CRYSTALS -REDISCOVERY OF THE SCHWARZ-HORA EFFECT, Physica. A, 233(3-4), 1996, pp. 655-662
We have discovered the laser-induced ''freezing'' of charged defects i
nto two-dimensional hexatic arrays in lead magnesium niobate. This sit
uation arises when, due to simultaneous thermal focussing and photoref
ractive phenomena, a holographic grating is produced that allows phase
-matched light scattering. The diffraction angle for the hexagonal pat
tern is Theta = 0.20 degrees, which agrees reasonably well with the th
eoretical value of 0.45 degrees from Firth's equation.