Asymmetric modulation of photorefractive space-charge fields formation: Theory and experimental validation

Abstract

The asymmetric modulation of light-induced space-charge fields by axial beam motion (v→∥opticalaxis) in Ce:SBN crystals was investigated through coupled theory-experiment approaches. Theoretically, introducing a direction-sensitive velocity term into the Kukhtarev equations yields analytical solutions that reveal electric field enhancement (v→<0) or attenuation (v→>0) due to asymmetric carrier accumulation, with the critical velocity v→c=μE→0 defining the threshold for dominance of these effects. Experimentally, 0.03 wt. % Ce:SBN demonstrates 81.8% diffraction efficiency gain under reverse motion vs 37.6% reduction in forward motion, while 0.1 wt. % crystals exhibit direction-triggered self-focusing, defocusing, and asymmetric oscillation. The unexpected dielectric breakdown observed at relatively high forward beam velocities (v→>0) directly confirms the simultaneous decay of the space-charge field and amplification of the external field. Theoretical predictions exhibited remarkable concordance with experimental observations, validating the proposed physical model. These findings establish a “velocity–direction–field” co-design paradigm enabling high-speed reconfigurable photonic devices.