Spatially Modulated Refractive Indices and Optical Filter Characteristics in the Light-Induced Metastable State of Na_2[Fe(CN)_5NO]·2H_2O

摘要

The metastable state of Na_2[Fe(CN)_5NO]·2H_2O crystals produced by irradiation with green or blue laser light was investigated using X-ray diffraction and spectroscopic methods. A thin crystalline plate in the metastable state placed between a pair of polarizers behaves like an optical filter. It works as the band-pass or band-reject filter, depending on the cross or parallel alignment of polarizers. A remarkable point of this effect is that the band center corresponds with the wavelength of the laser applied for producing the metastable state. This phenomenon is explained based on spatially modulated refractive indices produced by the photorefractive effect of laser irradiation. Numerical calculations using Berreman's 4 * 4 matrix method show that the spatially modulated population of the metastable anion exists even in the photostationary state. Similarity with the Solc birefringent filter is also discussed.