Temperature-dependent index-of-refraction changes in BaTiO_3

We investigate thermally induced changes in the index of refraction of BaTiO(3) that are caused by optical absorption. We show that the absorption of a 900-mW optical beam will change the surface temperature of a BaTiO(3) crystal by more than 40 degrees C and cause the extraordinary index of refraction to change by more than 10(-2). For a 900-mW beam incident upon a BaTiO(3) crystal that is not mounted on a heat sink, the surface temperature and the extraordinary index of refraction are still changing after more than 10 min. We also demonstrate that the thermally induced time-dependent index change is partially responsible for the frequency-shifted return from a two-internal-reflection or Cat self-pumped phase-conjugate mirror that has not reached thermal equilibrium.