Abstract

In an instability leading to pattern formation, the spectrum of fluctuations below the instability threshold is peaked around a wave number associated with the spatial periodicity of the pattern which is formed above threshold. In an isotropic system the far field displays a ring of maximum power. The selection of a discrete set of wavevectors within this ring is a nonlinear process in which the correlations among the wavevectors play a definite role. The discrete set of selected modes determine the pattern which is formed above threshold. Such correlations among the selected wavevectors have been recently considered [1] in pattern forming nonlinear optical systems and can be understood in terms of simultaneous emission of twin photons.

© 1998 IEEE