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 ${\text{Na}}_2\left[\text{Fe}{\left(\text{CN}\right)}_5\text{NO}\right]\cdot 2{\text{H}}_2\text{O}$ , ${\left({\text{CN}}_3{\text{H}}_6\right)}_2\left[\text{Fe}{\left(\text{CN}\right)}_5\text{NO}\right]$ , and $\text{Ba}\left[\text{Fe}{\left(\text{CN}\right)}_5\text{NO}\right]\cdot 3{\text{H}}_2\text{O}$ . With identically polarized recording beams thermal gratings are written by the thermo-optic effect, which results from the spatially modulated thermo-optic coefficient $\partial n/\partial T$ . The lifetime ${\tau }_{\text{dif}}$ of such gratings depends quadratically on the spatial grating frequency K with the thermal diffusion coefficient $D_{\text{dif}}$ as the material parameter: ${\tau }_{\text{dif}}=D_{\text{dif}}^{-1}{K}^{-2}$ . 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.