Enhanced photorefractive effect in SBN:60:Cr and SBN.60:Rh with external dc fields

Abstract

A major thrust of photorefractive materials research has been to increase the coupling constant Γ and speed up response time. Previous two-beam coupling experiments using SBN:60 have shown that the space charge field Esc, and therefore the coupling constant, can be increased to some degree by optimizing the characteristic fields En and Ed.1,2 However, since Esc tends toward the smaller of EN and Ed for no external field, any attempt to incrase Esc by increasing En will have minimal effect since Esc will be limited by the diffusion field Ed. By applying an external dc electric field E0, the photoexcited carriers will tend to be driven into the traps half a grating period away, and Esc will be limited by En = eNA/ϵK for large E0. Experimentally, Γ has been found to increase by almost a factor of 3 to over 10 cm−1 in Cr-doped SBN:60 with an applied field of 10 kV/cm. In addition, for Rh-doped SBN:60, the response time has been found to get significantly faster with an applied field, decreasing by more than an order of magnitude from ~2 s for E0 = 0 to 0.1 s with E0 = 10. These results suggest potential applications in field-enhanced optical limiting, switching, and thresholding.