Glass, optical glass, glass raw material for press molding, and optical element
A glass including at least one type of oxide selected from TiO 2 , Nb 2 O 5 , WO 3 , and Bi 2 O 3 as a glass component therefor, having a total TiO 2 , Nb 2 O 5 , WO 3 , and Bi 2 O 3 content of at least 20 mol %, and having a βOH value indicated in formula (1) that fulfills the relationship indicated in formula (2). βOH=−[ln( B/A )]/ t (1); βOH≧0.4891×ln(1/ HR )+2.48 (2).
1. An optical glass which is a phosphate glass comprising at least one oxide selected from the group consisting of TiO 2 , Nb 2 O 5 , WO 3 and Bi 2 O 3 as a glass component, wherein
a refractive index nd is 1.75 or more, and
a value of βOH shown in the below equation (1) satisfies the relation shown in the below equation (6);
βOH=−[ln( B/A )]/ t (1);
βOH≧181.39× nd −3 −325.75× nd −2 +194.85× nd −1 −38.1 (6);
in the equation (1), “t” is a thickness of said glass used for a measurement of an external transmittance, “A” is the external transmittance (%) at a wavelength of 2500 nm when a light enters into said glass in parallel to a thickness direction thereof, “B” is the external transmittance (%) at the wavelength of 2900 nm when a light enters into said glass in parallel to the thickness direction thereof, and “ln” is natural logarithm; in the equation (6), “nd” is the refractive index of said glass at the wavelength 587.56 nm.
2. The optical glass as set forth in claim 1 , wherein a content of P 2 O 5 is larger than a content of B 2 O 3 in terms of mol % expression.
3. The optical glass as set forth in claim 1 , wherein a content of TiO 2 is 1 mol % or more.
4. The optical glass as set forth in claim 1 , wherein a content of Sb 2 O 3 is 0 ppm or more and less than 1000 ppm.
5. The optical glass as set forth in claim 1 , wherein a content of Sb 2 O 3 is 0 ppm or more and 500 ppm or less.
6. The optical glass as set forth in claim 1 wherein substantially free of V.
7. The optical glass as set forth in claim 1 , wherein a content of noble metal is 4 ppm or less.
8. The optical glass as set forth in claim 1 , wherein a content of Pt is 2.0 ppm or less.
9. The optical glass as set forth in claim 1 , wherein the glass transition temperature Tg is 541° C. or more.
10. A glass material for press-molding comprising the optical glass as set forth in claim 1 .
11. An optical element comprising the optical glass as set forth in claim 1 .