Voronoi analysis of the breakdown of order in spontaneous optical spot patterns

In a nonlinear optical single feedback system, patterns of bright spots evolve spontaneously. Making use of the Voronoi construction, the breakdown of spatial order in experimental spot patterns under increase of the pump laser intensity is analyzed. The spot density is found to increase with the pump intensity. Our analysis shows that maximum order is maintained for a finite range of spot densities and starts to break down at a clearly detectable threshold value. The enhanced disorder with increasing density contrasts the behavior of simple hard-core systems. A separate analysis of the metrical properties of the Voronoi cells in ordered and disordered regions yields remarkably smaller nearest-neighbor distances in disordered regions. This suggests that the creation of new spots is a governing mechanism for the observed breakdown of order.