METHOD FOR MAKING LOW-STRESS LARGE-VOLUME NOT-(111)-ORIENTED CRYSTALS WITH REDUCED STRESS BIREFRINGENCE AND MORE UNIFORM REFRACTIVE INDEX AND CRYSTALS MADE THEREBY

摘要

A method is described for making an especially not-(111)-oriented low-stress large-volume crystal having a glide plane with reduced stress birefringence and more uniform refractive index. The method includes growing and tempering the crystal while heating and/or cooling to form a temperature gradient in order to relax stresses arising along the glide plane. During the tempering the heating and/or cooling occurs by heat transfer in a heat transfer direction and the heat transfer direction or temperature gradient is oriented at an angle of from 50° to 900° to the glide plane. Crystals with a uniform refractive index with variations of less than 0.025×10⁻⁶ (RMS value) are produced by the method.