We investigated both analytically and numerically the simultaneous influence of higher-harmonic gratings and subharmonic gratings on the threshold for generation of the subharmonic K/2 grating. The higher-harmonic grating causes feedback to the fundamental grating, thus leading to a nonlinear correction in dissipation, and the threshold for subharmonic generation is substantially modified by the presence of more subharmonics. The numerical solution shows that the inclusion of five higher-harmonic components and four subharmonic components are sufficient to cover the entire spatial region. The discrepancy between the analytical and the numerical solution increases with increased electric-field amplitude.
© 1999 Optical Society of America
(090.7330) Holography : Volume gratings
(160.5320) Materials : Photorefractive materials
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.5330) Nonlinear optics : Photorefractive optics
Per M. Johansen, Henrik C. Pedersen, Evgeny V. Podivilov, and Boris I. Sturman, "Ac square-wave field-induced subharmonics in photorefractive sillenite: threshold for excitation by inclusion of higher harmonics," J. Opt. Soc. Am. B 16, 103-110 (1999)