Optical element and method for producing the same

1. An optical element comprising: a optical glass made of a phosphate glass or a fluorophosphate glass; and an optically functional film formed on a surface of the optical glass,

wherein the optically functional film comprises a first layer and an outermost surface layer made of different materials,

and the outermost surface layer thereof is made of a material(s) having low reactivity with phosphoric acid,

wherein said optical glass is exposed at a side surface thereof.

2. The optical element according to claim 1 ,

wherein said first layer is at least one oxide film selected from the group consisting of Al 2 O 3 and a mixture of ZrO 2 and TiO 2 .

3. The optical element according to claim 1 , wherein the outermost surface layer of the optically functional film is an oxide film.

4. The optical element according to claim 3 , wherein the outermost surface layer is an oxide film which is made of at least one material selected from the group consisting of SiO 2 , Al 2 O 3 , Y 2 O 3 , La 2 O 3 , HfO 2 , Ta 2 O 5 , TiO 2 , ZrO 2 and Nb 2 O 5 .

5. The optical element according to any one of claims 2 to 4 , wherein the outermost surface layer of the optically functional film has a film thickness of 5 nm to 450 nm.

6. The optical element according to claim 1 , wherein said optical glass comprises:

45 to 53% by mass P 2 O 5 ,

7 to 37% by mass ZnO,

0 to 9% by mass K 2 O,

0 to 10% by mass Na 2 O,

1 to 4% by mass Li 2 O,

1 to 10% by mass Al 2 O 3 ,

0 to 10% by mass BaO,

0 to 5% by mass CaO, and

0 to 2% by mass of each of B 2 O 3 , SiO 2 , ZrO 2 , Sb 2 O 3 , SrO, La 2 O 3 , MgO, WO 3 and Nb 2 O 5 .

7. The optical element according to claim 1 , wherein said optical glass comprises:

36 to 48% by mass P 2 O 5 ,

4 to 11% by mass B 2 O 3 ,

3 to 5% by mass Li 2 O,

15 to 38% by mass BaO,

2 to 9% by mass CaO,

0 to 7% by mass MgO,

0 to 8% by mass SrO,

2 to 4% by mass Al 2 O 3 , and

0 to 4% by mass of each of ZnO, La 2 O 3 and Gd 2 O 3 .

8. The optical element according to claim 1 , wherein said optical glass comprises:

0 to 7% by mass P 2 O 5 ,

0 to 2% by mass NaF,

12 to 32% by mass AlF 3 ,

5 to 11% by mass MgF 2 ,

15 to 17% by mass CaF 2 ,

19 to 26% by mass SrF 2 ,

0 to 27% by mass Al(PO 3 ) 3 , and

14 to 15% by mass BaF 2 .

9. A method for producing the optical element according to claim 1 comprising forming an optically functional film comprising a first layer and an outermost surface layer made of different materials and sequentially laminated, on a surface of an optical glass made of a phosphate glass or a fluorophosphate glass,

wherein an outermost surface layer of the optically functional film is made of a material(s) having low reactivity with phosphoric acid.

10. The method for producing an optical element according to claim 9 , wherein the optically functional film is formed by a vacuum vapor deposition film forming method using an electron gun evaporation source.

11. The method for producing an optical element according to claim 10 , wherein the optically functional film is formed by a plasma-assist or ion-assist vapor deposition film forming method using an electron gun evaporation source.

12. The method for producing an optical element according to claim 9 , wherein the optically functional film is formed by a sputtering film forming method.

13. The method for producing an optical element according to any one of claims 9 to 12 , wherein the optical glass made of a phosphate glass or a fluorophosphate glass is obtained by softening an optical glass forming material by heating, and pressing it with a mold.