TiO<sub>2</sub>-SiO<sub>2</sub> glass is one of the leading candidates for optical elements of extreme ultraviolet lithography. TiO<sub>2</sub>-SiO<sub>2</sub> glass synthesized by the soot method has shown striae related to inhomogeneity of TiO<sub>2</sub> concentration formed in the planes perpendicular to soot growth direction in the synthesis process. It can induce CTE variation and localized surface roughness. Striae were characterized in three modes by polarization microscope. Such striae were improved with an improved gas condition and developing a modified material gas supply system. Specimen prepared from the improved TiO<sub>2</sub>-SiO<sub>2</sub> glass was evaluated by a line-focus-beam ultrasonic material characterization system, using a surface-acoustic-wave mode. Improved glass had 43% striae level compared to conventional glass by birefringence measurement, 31% compared to conventional glass by the ultrasonic measurement. It was found that improved glass had good homogeneity to both directions perpendicular and parallel to striae plane.
Macroporous titania (TiO<sub>2</sub>) monoliths have been prepared by the sol-gel method including phase separation, and the light-scattering properties have been investigated by means of coherent backscattering. Macroporous TiO<sub>2</sub> gels are obtained in the systems containing aqueous titania colloid and poly(ethylene oxide)(PEO). Threedimensionally interconnected macroporous structure is formed when the transient structure of phase separation is fixed as the permanent morphology by the sol-gel transition. The domain size of macroporous TiO<sub>2</sub> gels can be controlled reproducibly by adjusting the concentration of PEO. During the heat treatment above 1000 °C, the TiO<sub>2</sub> skeleton is sintered into fully dense body and the crystalline structure is transformed from anatase to rutile, while maintaining macroporous morphology. We show that the rutile-type TiO<sub>2</sub> -based macroporous monoliths are strongly scattering media for visible light.