SUBHARMONIC INSTABILITIES IN PHOTOREFRACTIVE CRYSTALS FOR AN APPLIED ALTERNATING ELECTRIC-FIELD - THEORETICAL-ANALYSIS

The spatial subharmonic instability arising from the material equation s is investigated theoretically for both square and sinusoidal applied alternating electric fields. The threshold conditions are given for t he amplitude of the applied field as a function of the detuning freque ncy, contrast of fundamental interference pattern, and interbeam angle by the use of the temporal solutions for the amplitude of the space-c harge field presented elsewhere [J. Opt. Soc. Am. B. 10, 124 (1993)] T he different effects of the square wave and sinusoidal applied fields for subharmonic generation are discussed.