SUBHARMONIC DOMAINS IN A BISMUTH-GERMANATE CRYSTAL

It is shown that a subharmonic grating may have two different phase re lationships relative to the fundamental grating, leading to the appear ance of domains. The subharmonic beam is generated in a Bi12GiO20 crys tal illuminated by two beams in the presence of an applied ac square-w ave voltage. The domain structure and the relative phases of the grati ngs contained in them have been observed with the aid of an interferom etric technique.