Influence of heat treatments on the spectral performance of a V-type double-layer antireflection coating at 1.06 microm.
The influence of heat treatment on the spectral performance of a V-type antireflection coating was studied. This coating was applied to ophthalmic glass windows for an Nd:YAG laser and consisted of two oxide layers designed to reduce the reflectance at 1.06 microm. Typical results show minimum reflectance of <0.1% at the required wavelength. The coated samples were heated in air to 300 and 500 degrees C and cooled to room temperature. A significant shift of the reflectance curve toward the short wavelengths and higher values of the reflectance at the minimum point was obtained dependent on the heating temperature. We found changes in the optical thicknesses and of the refractive indices of the layers. Considering these changes the coating with the same materials was redesigned to assure meeting specifications after heating. The experimental results show that this effect is mainly due to changes in the optical thicknesses and the refractive indices of the layers while contributions of other parameters could be neglected. The laser damage threshold of the redesigned coatings were >3 GW/cm(2).
Rabinovitch
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ELOP Electrooptics Industries, Ltd., P.O. Box 1165, Rehovot 76110, Israel.
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