Ca-SUBSTITUTED POLYCRYSTALLINE GARNETS WITH VERY LOW OPTICAL ABSORPTION

Abstract

Ca-substituted polycrystalline garnets with low optical absorption coefficient, below 2 cm-I, can be reproducibly prepared by reducing the cause of dispersion and absorption.The lowest optical absorption coefficient which has been measured so far is 0.5 cm-1 at the wavelength of 1.55 ~m. Reduction of porosity can be accomplished by simultaneous substitution of y3+ ions by Ca 2 +ions in combination with V S + ions for charge compensation and by sintering near the temperature at which the anomalous grain growth originates. Also, heat treatment at the temperature in the normal grain growth region reduces optical absorption of CaV-substituted polycrystalline garnets. It was found that the dispersion effect on optical absorption caused by grains is small in comparison with the dispersion caused by pores.