Optical member for deep ultraviolet and process for producing same

1. An optical member comprising:

a synthetic silica glass which does not substantially contain a halogen element, has a maximum OH group content of less than 10 ppm by weight, has contents of an oxygen deficient center and an E-prime center of each less than 1×10 14 cm −3 , does not substantially contain SiH and peroxy linkage, and has a fictive temperature of 1,050° C. or lower,

wherein the synthetic silica glass is transparent to a deep ultraviolet light having a wavelength of 250 nm or shorter.

2. The optical member according to claim 1 , wherein variation in the fictive temperature in the synthetic silica glass is 5° C. or less.

3. A process for producing the optical member according to claim 1 ,

wherein the process comprises:

synthesizing a porous synthetic silica glass body having a volume average bulk density of 0.33 g·cm −3 or more, the synthesizing comprising growing glass fine particles by a flame hydrolysis reaction of a raw material comprising a silicon compound;

pre-sintering the porous synthetic silica glass body after the synthesizing;

subjecting the porous synthetic silica glass body to a heat treatment at a temperature in a range of from 1,050 to 1,250° C. for more than 90 hours in vacuum at a pressure of 1×10 −2 Pa or less; and

performing a transparent vitrification of the porous synthetic silica glass body to obtain the synthetic silica glass.

4. The process according to claim 3 , wherein the porous synthetic silica glass body synthesized has a variation in the bulk density of 0.1 g·cm −3 or less.

5. A process for producing the optical member according to claim 2 ,

wherein the process comprises:

synthesizing a porous synthetic silica glass body having a volume average bulk density of 0.33 g·cm −3 or more, the synthesizing comprising growing glass fine particles by a flame hydrolysis reaction of a raw material comprising a silicon compound;

pre-sintering the porous synthetic silica glass body after the synthesizing;

subjecting the porous synthetic silica glass body to a heat treatment at a temperature in a range of from 1,050 to 1,250° C. for more than 90 hours in vacuum at a pressure of 1×10 −2 Pa or less; and

performing a transparent vitrification of the porous synthetic silica glass body to obtain the synthetic silica glass.

6. The process according to claim 5 , wherein the porous synthetic silica glass body synthesized has a variation in the bulk density of 0.1 g·cm −3 or less.

7. The process according to claim 3 , wherein the porous synthetic silica glass body having the volume average bulk density of the 0.37 g·cm −3 or more is synthesized before the pre-sintering.

8. The process according to claim 7 , wherein the pressure in the heat treatment is 3×10 −3 Pa or less.

9. The process according to claim 8 , wherein the pressure in the heat treatment is 1×10 −3 Pa or less.

10. The process according to claim 9 , wherein the temperature in the heat treatment is in a range of from 1,100 to 1,200° C.

11. A process for producing an optical member, comprising:

synthesizing a porous synthetic silica glass body having a volume average bulk density of 0.33 g·cm −3 or more, the synthesizing comprising growing glass fine particles by a flame hydrolysis reaction of a raw material comprising a silicon compound;

pre-sintering the porous synthetic silica glass body after the synthesizing;

subjecting the porous synthetic silica glass body to a heat treatment at a temperature in a range of from 1,050 to 1,250° C. for more than 90 hours in vacuum at a pressure of 1×10 −2 Pa or less; and

performing a transparent vitrification of the porous synthetic silica glass body to obtain a synthetic silica glass.

12. The process according to claim 11 , wherein the porous synthetic silica glass body having the volume average bulk density of the 0.37 g·cm −3 or more is synthesized before the pre-sintering.

13. The process according to claim 12 , wherein the pressure in the heat treatment is 1×10 −3 Pa or less.

14. The process according to claim 13 , wherein the temperature in the heat treatment is in a range of from 1,100 to 1,200° C.

15. An optical member produced by the process according to claim 11 , wherein the synthetic silica glass does not substantially contain a halogen element, has a maximum OH group content of less than 10 ppm by weight, has contents of an oxygen deficient center and an E-prime center of each less than 1×10 13 cm −3 , does not substantially contain SiH and peroxy linkage, and has a fictive temperature of 1,050° C. or lower.

16. The optical member according to claim 15 , wherein variation in the fictive temperature in the synthetic silica glass is 1° C. or less.

17. The optical member according to claim 1 , wherein the synthetic silica glass has the maximum OH group content of 5 ppm by mass or less and 1 ppm by mass or more.

18. The optical member according to claim 17 , wherein the fictive temperature is 1,020° C. or lower.

19. The optical member according to claim 17 , wherein variation in the fictive temperature in the synthetic silica glass is 1° C. or less.

20. The optical member according to claim 17 , wherein the contents of the oxygen deficient center and the E-prime center in the synthetic silica glass are each less than 1×10 13 cm −3 .