Phase gratings in the visible and near-infrared spectral range realized by metastable electronic states in Na-2[Fe(CN)(5)NO]center dot 2H(2)O

Abstract

Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitroPrusside (SNP), Na-2[Fe(CN)(5)NO]. 2H(2)O, single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the [Fe(CN)(5)NO](2-) anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more than Delta n = 1 x 10(-3) in the red (632.8 nm) and Delta n = 5 x 10(-4) in the near-infrared region (1047 nm). The absorption coefficient is modulated by about Delta alpha = 100 m(-1) at 632.8 mm and 40 m(-1) at 1047 nm. The wavelength dependence of Delta n 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 eta 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.