Optical absorption of liquid phase epitaxial garnet films at 1.3-μm wavelength for magneto-optic application

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Abstract
Optical absorption of liquid phase epitaxial magneto‐optic Gd0.2Y2.8Fe5O12 films was measured at 1.3‐μm wavelength using a waveguide technique. An optical absorption coefficient of α=0.2 cm−1 at 1.3 μm was obtained. This is the smallest value which has ever been reported for a garnet film and corresponds to 230 deg/dB in the figure of merit for Gd:YIG with the Faraday rotation coefficient of 200 deg/cm. α≤0.6 cm−1 is obtained, when garnet films are grown under the supercooling temperature of less than 10 °C. The supercooling temperature dependence of the α value is more insensitive for films grown from melts poor in B2O3 than for films from B2O3 rich melts. A mechanism of increase in optical absorption is discussed from the viewpoint of lead ion condensation at the solid/liquid interface and of incorporation into garnet films.