Dispersion of the photoanisotropy induced in anFA(II) KCl:Li crystal

The dichroism and birefringence photoinduced in an $F_A$(II) KCl:Li crystal by a linearly polarized light beam are theoretically analyzed, taking into account the off-axis position of the ${\mathrm{Li}}^{+}$ ion inside the crystal. Measurements are taken between 400 and 700 nm, the crystal being at liquid-nitrogen temperature. The peculiar shapes of the resulting curves are discussed. The value of the angular shift θ of the ${\mathrm{Li}}^{+}$ ion is deduced from the curves corresponding to the saturation, taking into account the wavelength of the exciting light. We found θ=17°±1° for a crystal at liquid-nitrogen temperature.