Pulse recording of thermal and linkage isomer gratings in nitrosyl compounds

Abstract

Two different kinds of short-lived phase gratings are written with identically and orthogonally polarized waves using nanosecond laser pulses in single crystals of the nitrosyl compounds Na2[Fe(CN)5NO]⋅2H2O, (CN3H6)2[Fe(CN)5NO], and Ba[Fe(CN)5NO]⋅3H2O. With identically polarized recording beams thermal gratings are written by the thermo-optic effect, which results from the spatially modulated thermo-optic coefficient ∂n/∂T. The lifetime τdif of such gratings depends quadratically on the spatial grating frequency K with the thermal diffusion coefficient Ddif as the material parameter: τdif=Ddif−1K−2. Upon recording with mutually orthogonally polarized beams no intensity modulation occurs, but the resulting modulation of the polarization leads to the generation of light-induced linkage NO-isomers with varying efficiency according to the local state of the light polarization. This rotation of the NO ligand by nearly 90° results in a modulation of the polarizability and with this of the refractive index of the crystal.