Reducing Treatment Effects on Absorption Loss in (BiGdCa)3(FeAlGa)5O12 Films

The absorption loss of (BiGdCa)3(FeAlGa)5O12 films is discussed. In the films grown at a growth temperature (Tg) in the range 745 to 764°C, the absorption loss was 1 ~ 3 dB/cm. It was conjectured that the increase in the absorption loss of the films grown below Tg = 740°C was due mainly to film defects. Absorption loss for this Bi-substituted garnet film was almost equal to that for reduction treated Ca:YIG with low impurity density at ¿ = 1.15 ¿m, but at ¿ = 0.79 ¿m the Bi-substituted garnet film absorption loss was 220 dB/cm and it was almost twice that of the Ca:YIG film. The increase in absorption loss at 0.79 ¿m seems to be due to the fact that when Bi and Pb are substituted, the absorption edge for the film shifts to longer wavelengths and extends as far as the 0.79 ¿m wavelength.