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 SodiumNitro-Prusside (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 thanΔn = 1 × 10⁻³ in the red (632.8 nm) andΔn = 5 × 10⁻⁴ in the near-infrared region (1047 nm). The absorption coefficient is modulated by aboutΔα = 100 m⁻¹ at 632.8 nm and 40 m⁻¹ at 1047 nm. The wavelength dependence ofΔn 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 efficiencyη 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 thea- andb-axis of the orthorhombic system.