Phase gratings in the visible and near-infrared spectral range realized by metastable electronic states in Na2[Fe(CN)5NO]·2H2O

Abstract

Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitroPrusside (SNP), Na2[Fe(CN)5NO]·2H2O, single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the [Fe(CN)5NO]2-anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more than Δn = 1 × 10-3 in the red (632.8 nm) and Δn = 5 × 10-4 in the near-infrared region (1047 nm). The absorption coefficient is modulated by about Δα = 100 m-1 at 632.8 nm and 40 m-1 at 1047 nm. The wavelength dependence of Δn can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiency η depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along the a- and b-axis of the orthorhombic system.