A three mirror cavity for a magneto-optic light deflector

Magnetic stripe domains in thin crystals of the class bismuth substituted rare earth iron garnet can be used to diffract light from visible and near infrared lasers. The stripe domains form a Faraday effect phase grating which is alterable in solid state fashion by externally applied magnetic fields in such a way that the deflected laser light is controllably moved over a sector of a plane. In order to take full advantage of this effect in thin crystals at the 1.06μm Nd-YAG laser line, it is convenient to place the crystal inside an optical cavity operated in the multipass, anti-resonant mode. The laser light becomes a standing wave inside the cavity and much higher deflection efficiency is obtainable. For instance, a 20 micron sample which normally deflects less than 1/2 percent of an incident 1.06 micron laser beam was found to deflect 10 percent of the beam when operated in the multipass mode.