A fully nonlinear frequency response of a moving grating in bismuth silicon oxide, including the effects of an applied electric field, is modeled by solution of the time-dependent Kukhtarev equations for photorefractive materials. The numerical results are used to define fully the nonlinear response function F(m)=a<sup>-1</sup>[1-exp(-am)], where m is the modulation index in the intensity pattern, to yield the unknown quantity a over a broad range of detuning frequencies f . For low f, the response is superlinear with a<0, and for relatively large f it is sublinear with a>0 . In the midrange we predict, for the first time to our knowledge, a characteristic frequency f<sub>l</sub> at which a=0 and the response is linear, that is, F(m)≈m, despite the presence of nonlinearly generated higher harmonics of the fundamental grating wave number. In view of this linear behavior, writing a hologram at the linear-response frequency f<sub>l</sub> might permit a more faithful reproduction of an object than that which is possible by writing at the frequency of maximum response at the resonance.
© 1999 Optical Society of America
Tony Gatlin and Nagendra Singh, "Nonlinear frequency response of a moving grating with an applied field in bismuth silicon oxide," Opt. Lett. 24, 1593-1595 (1999)