Effect of hydrostatic pressure on the refractive indices of some solids

M easurem ents were m a de on r efractive index changes with h yd ro static pressures between 1 ba r a nd 1 kbar usin g the h elium yellow line . Thc ma te rials studies were: KBr NaCI, LiF, diamond, MgO, quartz, A120 3, a nd t hree silicate glasses. All t he materials increased in refractive index with pressure except diamond, M gO, a nd Alz03 which decreased, a nd LiF which did not change. The results we re compared with photoelastic m easurem ents, a nd Pockel's geo m etric t heory of phot oelasticity was substantiated as well as Muell er's physica l theory. The data show that the ra t io of change of polari za bili ty wi t h density is greater for solids having stron ger interatomi c r epulsive forc es. Volume and temperature coefficients of polari za bili ty were evaluated for the cubic crystals a nd glasses. The t hermooptic behavior of crysta ls and glasses is di scu ssed.