PRESSURE-DEPENDENCE OF THE REFRACTIVE-INDEX AND ELECTRONIC POLARIZABILITY OF LIF, MGF2 AND CAF2

The pressure dependence of the refractive index of LIF, MgF2 and CaF2 was measured up to 8 GPa using an interferometric method with the diam ond anvil cell. Despite the different crystalline structures, a simila r increasing behavior of n(P) for the three compounds under considerat ion was observed, indicating that the fluorine ion should have an impo rtant role in the volume dependence of the optical properties of these materials. The respective variations of the electronic polarizabiliti es were determined by the Lorentz-Lorenz approach and they are represe nted by the following Mueller parameters: for LiF, Lambda(0) = 0.65, f or MgF2, Lambda 0 = 0.71 and for CaF2, Lambda(0) = 0.55. Some empirica l models found in the literature relating to the electronic polarizabi lity and the interatomic distance, were examined but one of them adequ ately describe the observed behavior.