Patent Number: 050420593
Section: claims

1. An optical element which is adapted for use in a radiation optical system having a radiation source and a means for receiving radiation generated from the radiation source and passing through the optical element, said optical element comprising a graphite film obtained by pyrolyzing a film of a polymer selected from the group consisting of polyphenylene oxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene-isophthalamide, polyphenylene-benzoimidazole, polyphenylene-benzobisimidazole, polythiazole and poly-p-phenylene-vinylene at a first temperature of not higher than 2800.degree. C. and at a first pressure of not higher than 20 kg/cm.sup.2, and subsequently at a second temperature higher than 2800.degree. C. and at a second pressure higher than 20 kg/cm.sup.2. 2. An optical element according to claim 1, wherein said polymer is polyphenylene oxadiazole. 3. An optical element according to claim 1, wherein said polymer is polypyromellitimide. 4. An optical element according to claim 1, wherein said graphite film is formed on to a flat substrate. 5. An optical element according to claim 1, wherein said graphite film is formed on a cylindrically curved substrate on the inner surface thereof. 6. An optical element according to claim 1, wherein a plurality of said polymer films are stacked to provide a block of graphite films. 7. An optical element according to claim 1, wherein a plurality of graphite films which have been obtained by pyrolyzing a plurality of polymer films at a temperature of not lower than 2800.degree. C. under a pressure of not lower than 4 kg/cm.sup.2, are combined to provide a graphite block. 8. An optical element which is adapted for use in a radiation optical system having a radiation source and a means for receiving a radiation generated from the radiation source and passing through an optical element, said optical element comprising a graphite film which is obtained by pyrolyzing at a temperature of not lower than 2800.degree. C., in vacuum or in an inert gas, a film of a polymer selected from the group consisting of polyphenylene oxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene isophthalamide, polyphenylene benzoimidazole, polyphenylene benzobisimidazole, polythiazole and poly-p-phenylene-vinylene and which has a metal halide intercalated therein. 9. An optical element according to claim 8, wherein said metal halide is intercalated in a first-stage condition where said metal halide is present in individual space between any adjacent lattice layers of said graphite film. 10. An optical element according to claim 8, wherein said metal halide is intercalated in a second-stage condition where said metal halide is present in every third space of lattice layers of said graphite film. 11. An optical element according to claim 8, wherein said metal halide is at least one member selected from the group consisting of BCl.sub.3, MgCl.sub.2, AlCl.sub.3, ScCl.sub.3, TiCl.sub.4, CrCl.sub.3, MnCl.sub.2, FeCl.sub.3, CoCl.sub.2, NiCl.sub.2, CuCl.sub.2, ZnCl.sub.2, GaCl.sub.3, YCl.sub.3, NbCl.sub.5, MoCl.sub.5, RhCl.sub.3, PdCl.sub.2, CdCl.sub.2, RuCl.sub.3, ZrCl.sub.4, InCl.sub.3, HfCl.sub.4, TaCl.sub.5, WCl.sub.6, ReCl.sub.4, OsCl.sub.4, PtCl.sub.4, AuCl.sub.3, HgCl.sub.2, TlCl.sub.3, BiCl.sub.4, ICl, IBr, FeCl.sub.2, BF.sub.3, AlBr.sub.3, SiF.sub.4, TiF.sub.4, FeBr.sub.3, CuBr.sub.2, PF.sub.6, GaBr.sub.3, NbF.sub.5, MoF.sub.6, CdBr.sub.2, TaF.sub.6, WF.sub.6, OsF.sub.3, AuBr.sub.3 and TlBr.sub.3. 12. An optical element according to claim 11 wherein said metal halide is CuCl.sub.2. 13. An optical element according to claim 11, wherein said metal halide is NiCl.sub.2. 14. An optical element according to claim 8, wherein a plurality of the intercalated graphite films are bonded together to form a sheet or block. 15. An optical element according to claim 8, wherein the intercalated graphite film is formed on a flat substrate. 16. An optical element according to claim 8, wherein intercalated graphite film is formed on a curved substrate at the inner side thereof. 17. An optical element which is adapted for use in a radiation optical system having a radiation source and a means for receiving a radiation generated from the radiation source and passing through an optical element, said optical element comprising at least one graphite film and at least one graphite film intercalated with a metal halide, both films being bonded together by pressing. 18. An optical element according to claim 17, wherein a plurality of the graphite films and a plurality of the intercalated graphite films which are alternately superposed and bonded together by pressing to form a sheet so that the graphite films are placed as an outermost layer on opposite sides. 19. An optical element according to claim 17, wherein a plurality of intercalated graphite films are sandwiched between two graphite films and bonded together by pressing to form a sheet. 20. An optical element according to claim 17, wherein said at least one graphite film is obtained by pyrolyzing at a temperature of not lower than 2800.degree. C. at a normal pressure in vacuum or in an inert gas a film of a polymer selected from the group consisting of polyphenylene oxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene-isophthalamide, polyphenylene-benzoimidazole, polyphenylene-benzobisimidazole, polythiazole and poly-p-phenylene-vinylene. 21. An optical element according to claim 17, wherein said at least one graphite film is obtained by pyrolyzing at a temperature of not lower than 2800.degree. C. at a pressure of not lower than 4 kg/cm.sup.2 in vacuum or in an inert gas a film of a polymer selected from the group consisting of polyphenylene oxadiazole, polyimide, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene-isophthalamide, polyphenylene-benzoimidazole, polyphenylene-benzobisimidazole, polythiazole and poly-p-phenylene-vinylene. 22. An optical element according to claim 17, wherein said at least one graphite film intercalated with the metal halide is a product which is obtained by pyrolyzing at a temperature of not lower than 2800.degree. C. in vacuum or in an inert gas a film of a polymer selected from the group consisting of polyphenylene oxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene-isophthalamide, polyphenylene-benzoimidazole, polyphenylene-benzobisimidazole, polythiazole and poly-p-phenylene-vinylene and intercalating the resultant graphite film with a metal halide. 23. An optical element according to claim 22, wherein said metal halide is at least one member selected from the group consisting of BCl.sub.3, MgCl.sub.2, AlCl.sub.3, ScCl.sub.3, TiCl.sub.4, CrCl.sub.3, MnCl.sub.2, FeCl.sub.3, CoCl.sub.2, NiCl.sub.2, CuCl.sub.2, ZnCl.sub.2, GaCl.sub.3, YCl.sub.3, NbCl.sub.5, MoCl.sub.5, RhCl.sub.3, PdCl.sub.2, CdCl.sub.2, InCl.sub.3, HfCl.sub.4, TaCl.sub.5, WCl.sub.6, ReCl.sub.4, OsCl.sub.4, PtCl.sub.4, AuCl.sub.3, HgCl.sub.2, TlCl.sub.3 and BiCl.sub.4. 24. An optical element according to claim 17, wherein the bonded films are formed on a flat substrate. 25. An optical element according to claim 17, wherein the bonded films are formed on a cylindrically curved substrate.