Ferroelectric material, two-color holographic recording medium and the wavelength selective filter

摘要

A ferroelectric material in which the refractive index change can be induced by irradiation with light at two different wavelengths without performing a reduction treatment or doping impurities. The ferroelectric material of the invention in which the refractive index change is induced by irradiation with light at two different wavelengths is a lithium tantalate single crystal with the composition of Li2O/(Li2O+Ta2O5)=0.4966 to 0.4995. Preferably, the ferroelectric material is a lithium tantalate single crystal with the composition of Li2O/(Li2O+Ta2O5)=0.4974 to 0.4989. Preferably, the infrared absorption coefficient in the [OH] stretching mode falls within a range of 0 cm-1 to 0.15 cm-1 (0 cm-1 and 0.15 cm-1 are included in the range).