Optical glass suffering little change in refractive index by radiation of light

1. An optical glass consisting of, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–less than 15%

PbO

0–2%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

wherein the total amount of the CaO, SrO and Zr 2 ingredients is 2% or less and Na 2 O+K 2 O+BaO+ZnO in the total amount of 10–45% TiO 2 0–0.5% and fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11%, said optical glass including a fluorine ingredient and/or a titanium oxide ingredient and/or an arsenic oxide ingredient.

2. An optical glass as defined in claim 1 wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

3. An optical glass as defined in claim 2 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient an/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

4. An optical glass comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–20%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

19.5–45%

where

BaO

1.19–42%

TiO 2

0–0.5% and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11% wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

5. An optical glass as defined in claim 4 further comprising, in mass %,

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

The total amount of one or more of the CaO, SrO and ZrO 2 ingredients being 2% or below.

6. An optical glass as defined in claim 4 comprising a titanium oxide ingredient and/or an arsenic oxide ingredient.

7. An optical glass as defined in claim 6 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient and/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

8. An optical glass comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–20%

PbO

0–2%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

10–45%

where

BaO

1.19–42%

TiO 2

0–0.5% and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11% wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 mm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

9. An optical glass as defined in claim 8 further comprising, in mass %,

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

the total amount of one or more of the CaO, SrO and ZrO 2 ingredients being 2% or below.

10. An optical glass as defined in claim 8 comprising a titanium oxide ingredient and/or an arsenic oxide ingredient.

11. An optical glass as defined in claim 10 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient and/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

12. An optical glass comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–less than 15%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

10–45%

where

Na 2 O

0–13%

K 2 O

0–12%

BaO

1.19–42%

and

ZnO

0–7%

PbO

0–2%

TiO 2

0–0.5%

As 2 O 3

0–1%

Sb 2 O 3

0–1% and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11% wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 35 mm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

13. An optical glass as defined in claim 12 further comprising, in mass %,

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

the total amount of one or more of the CaO, StO and ZrO 2 ingredients being 2% or below.

14. Optical glass as defined in claim 12 comprising a titanium oxide ingredient and/or an arsenic oxide ingredient.

15. An optical glass as defined in claim 14 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient and/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

16. An optical glass comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–20%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–3%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

19.5–45%

where

Na 2 O

0–13%

K 2 O

0–12%

BaO

1.19–42%

and

ZnO

0–7%

PbO

0–2%

TiO 2

0–0.5%

As 2 O 3

0–1%

Sb 2 O 3

0–1% and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11% wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

17. An optical glass as defined in claim 16 further comprising, in mass %,

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

the total amount of one orc more of the CaO, SrO and ZrO 2 ingredients being 2% or below.

18. An optical glass as defined in claim 16 comprising a titanium oxide ingredient and/or an arsenic oxide ingredient.

19. An optical glass as defined in claim 18 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient and/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

20. An optical glass comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–20%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

10–45%

where

Na 2 O

0–13%

K 2 O

0–12%

BaO

1.19–42%

and

ZnO

0–7%

PbO

0–2%

TiO 2

0–0.5%

As 2 O 3

0–1%

Sb 2 O 3

0–1% and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 8.4–11% wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

21. An optical glass as defined in claim 20 further comprising, in mass %,

CaO

0–2%

SrO

0–2%

ZrO 2

0–2%

the total amount of one or more of the CaO, SrO and ZrO 2 ingredients being 2% or below.

22. An optical glass as defined in claim 20 comprising a titanium oxide ingredient and/or an arsenic oxide ingredient.

23. An optical glass as defined in claim 22 comprising, in mass %, 0.001–0.5% of TiO 2 as the titanium oxide ingredient and/or 0.001–1% of As 2 O 3 as the arsenic oxide ingredient.

24. A method of providing an optical glass for lenses of an optical system of an i-line stepper, said method comprising providing in said i-line stepper a lens made from en optical glass having a composition comprising, in mass %,

SiO 2

55.35–70%

B 2 O 3

3–less than 15%

PbO

0–2%

Al 2 O 3

0–2.3%

Li 2 O

0–3%

CaO

0–2%

Na 2 O + K 2 O + BaO + ZnO in the total amount of

10–45%

and

fluoride or fluorides substituting for the above oxide or oxides partially or entirely, a total amount of F contained in the fluoride or fluorides being 0–11%.