Abstract

We found that the extinction coefficient of ion-beam-sputtered titanium dioxide films first decreased with increasing annealing temperature then increased drastically when annealing temperature was increased above $\sim 200 °\mathrm{C}$ for 24 h of annealing time. The decreasing extinction coefficient with annealing temperature was attributed to a reduction in absorption owing to oxidation of the film by annealing. The film structure remained amorphous to 200 °C annealing temperature. The drastic increase of extinction coefficients above $\sim 200 °\mathrm{C}$ was associated with the appearance of an anatase polycrystalline structure and was attributed to scattering by the polycrystalline structure. With shorter annealing time the transition temperature from amorphous to polycrystalline anatase was higher. Guidance for reducing the optical loss of laser mirrors is proposed.

© 1998 Optical Society of America

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