Optically induced gratings have been created in Bi4Ge 3O12 single crystals doped with Fe and Mn impurities. The writing kinetics of the holograms depends on the previous illumination with ultraviolet (UV) light, λ=310 nm. It has been concluded that there is a photorefractive contribution due to Fe impurities ([Fe]=2.7×10 17 atoms/cm3) which can be observed when the holograms are written with 457.9 nm light. This contribution is essentially independent of the previous UV illumination, the steady state diffraction efficiency η of a 633 nm He-Ne laser beam is ≊2×10-4, and the corresponding modulation of the refractive index Δn at λ=633 nm is ≊4×10-6. The UV illumination induces a transient behavior of the diffraction efficiency with ηmax≊8×10 -4, this regime is dominated by the photorefractive effect. After this maximum, η decreases to ≤0.3×10-4 and a quasi steady state is reached; in this steady state regime the contribution of a photochromic grating dominates the value of η. Mn-doped samples ([Mn]=4.3×1017 atoms/cm3) also show the transient behavior and the photochromic contribution.
ASJC Scopus subject areas
- Physics and Astronomy(all)