Competition of hexagonal and square patterns in a photorefractive feedback system

Abstract

Square and squeezed hexagonal patterns have been observed for the first time in an optical pattern formation experiment very recently by the authors of this presentation [1]. The experimental setup consists of a reflection-grating dominated photorefractive phase conjugator and a feedback path containing an ordinary mirror and a thin imaging lens at distance 2f from the photorefractive crystal and distance 2f + L from the mirror. The schematic of the setup is shown in fig. 1.