KINETICS OF PHOTOREFRACTIVE GRATING FORMATION WITH AN EXTERNAL APPLIED-FIELD AT LARGER MODULATION DEPTHS

In this paper, we use the 'hopping' model to analyze the dynamic behav iors of the first three-order harmonics of the space-charge field at l arge modulation with an external de and ac field, respectively. We pre sent the respective exact and approximate dynamic analytical solutions in the presence of a de field and a sinusoidal ac field. For a suppli ed de field, the real parts of the first three-order harmonics of the space-charge field will decrease with increasing spatial frequency, bu t the imaginary part of each higher-order harmonic displays maximal va lues at the respective spatial frequencies. There are peak values for the real parts of the higher-order harmonics with increasing external electric fields: but no peak values for the real part of the fundament al harmonics and every imaginary part. For the applied sc field, we pr esent for the first time the approximate analytical solution of the fu ndamental harmonic, and found that the real part of the fundamental sp ace-charge field varies at the same frequency as that of the applied f ield, the imaginary part oscillates at twice that frequency. These res ults are in agreement with those derived from the band-transport model . (C) 1998 Elsevier Science B.V.