Optical member comprising TiO

1. An optical member comprising a TiO 2 -containing silica glass having: a TiO 2 concentration of from 3 to 10% by mass; a Ti 3+ concentration of 100 wt ppm or less and greater than 0 ppm; a thermal expansion coefficient at from 0 to 100° C., CTE 0-100 , of 0±150 ppb/° C.; and an internal transmittance in the wavelength region of 400 to 700 nm per a thickness of 1 mm, T 400-700 , of 80% or more, wherein the optical member has a ratio of variation of Ti 3+ concentration to an average value of the Ti 3+ concentration, ΔTi 3+ /Ti 3+ , on an optical use surface, of 0.2 or less.

2. The optical member according to claim 1 , comprising a TiO 2 -containing silica glass that contains F and has an F concentration of 1,000 wt ppm or more.

3. The optical member according to claim 1 , comprising a TiO 2 -containing silica glass having an OH concentration of 600 wt ppm or less.

4. The optical member according to claim 1 , comprising a TiO 2 -containing silica glass having an internal transmittance in the wavelength range of 300 to 3,000 nm per a thickness of 1 mm, T 300-3,000 , of 70% or more.

5. The optical member according to claim 2 , comprising a TiO 2 -containing silica glass having a ratio of variation of F concentration to an average value of the F concentration, ΔF/F, on an optical use surface, of 0.2 or less.

6. The optical member according to claim 1 , comprising a TiO 2 -containing silica glass having a distribution of temperature at which a thermal expansion coefficient is zero, ΔCOT, falling within a range of 5° C.

7. A process for carrying out EUV lithography comprising employing the optical member according to claim 1 as a photo mask or as a mirror.

8. A process for producing an optical member comprising a TiO 2 -containing silica glass that has a ratio of variation of Ti 3+ concentration to an average value of the Ti 3+ concentration, ΔTi 3+ /Ti 3+ , on an optical use surface of 0.2 or less, containing F, and having an F concentration of 1,000 wt ppm or more, which process comprises:

depositing and growing quartz glass fine particles obtainable by flame hydrolysis of glass-forming raw materials on a substrate, to thereby form a porous glass body;

keeping said porous glass body in a reaction vessel filled with elemental fluorine (F 2 ) or a mixed gas obtained by diluting elemental fluorine (F 2 ) with an inert gas, to thereby obtain a fluorine-containing porous glass body; and

subjecting said fluorine-containing porous glass body to temperature increase to a transparent vitrification temperature, to thereby obtain a fluorine-containing transparent glass body.

9. The optical member according to claim 1 , wherein ΔTi 3+ /Ti 3+ is 0.15 or less.

10. The optical member according to claim 1 , wherein ΔTi 3+ /Ti 3+ is 0.1 or less.

11. The optical member according to claim 1 , wherein ΔTi 3+ /Ti 3+ is 0.05 or less.

12. The optical member according to claim 1 , wherein the TiO 2 concentration is from 6 to 8% by mass.

13. The optical member according to claim 1 , wherein T 400-700 is 90% or more.

14. The optical member according to claim 4 , wherein T 300-3000 is 80% or more.

15. The optical member according to claim 1 , wherein the Ti 3+ concentration is 20 wt ppm or less.

16. The optical member according to claim 6 , wherein ΔCOT is 1° C. or less.

17. The optical member according to claim 3 , wherein the OH concentration is 30 ppm or less.

18. The optical member according to claim 1 , which has a fictive temperature of 1,100° C. or lower.

19. The optical member according to claim 1 , which has a fictive temperature of 850° C. or lower.