Claims
- 1. A method for reducing damage to an optic, comprising the steps of:
preparing said optic by a finishing process that minimizes subsurface defects and removes surface contaminants, laser conditioned said optic by exposing it to low fluences below levels that normally lead to the initiation and catastrophic growth of damage, and irradiating said optic at its high fluence design limit so that the concentration of damage sites that form on said optic is reduced.
- 2. The method of claim 1 wherein said advanced finishing process comprises the steps of:
application of conventional grinding and polishing to the surface of said optic to attain the desired, or near desired surface optical figure, application of a finishing step to the surface of said optics to remove the polishing layer and the subsurface damage left on the optic by the said conventional grinding and polishing, and application of an etching step to the surface of said optic to remove any contamination arising from the said finishing step.
- 3. The method of claim 2 wherein the said finishing step, and the said grinding and polishing step, are accomplished with the same tool.
- 4. The method of claim 2 wherein the said conventional grinding is accomplished with a standard optical shop abrasive grinding, such as blanchard or lap grinding, that brings the optics to gross desired dimensional shape.
- 5. The method of claim 2 wherein the said conventional polishing is accomplished by conventional lap polishing using a standard optic shop synthetic-bed or pitch-bed tools containing sequentially smaller sizes of wet abrasive media, such as cerium oxide or zirconium oxide slurries until the desired or near desired optical surface quality and figure are attained.
- 6. The method of claim 2 wherein the said polishing is adjusted to minimize the polishing layer that is composed of redeposited optical material and slurry.
- 7. The method of claim 2 wherein the said polishing is adjusted to minimize the subsurface damage layer that is composed of a network of medial and traversing cracks resulting from high normal stresses imparted by the polishing process.
- 8. The method of claim 2 wherein the said finishing step is accomplished by application of magnetorheological finishing tool to the surface of said optic to remove the polishing layer and the subsurface damage left on said optic by the grinding and polishing processes.
- 9. The method of claim 2 wherein the said polishing step is accomplished by application of magnetorheological polishing tool to the surface of said optic to attain the desired, or near desired surface optical figure.
- 10. The method of claim 2 wherein the said polishing and finishing steps are accomplished by application of a zirconia-based polishing tool.
- 11. The method of claim 2 wherein the said finishing step is accomplished using selected abrasives that leave little to no crack formation and propagation in the optics.
- 12. The method of claim 2 wherein the said etching step is accomplished using a fluoride solution composed of HF, NH4F and deionized water.
- 13. The method of claim 12 wherein different HF solution types and concentrations are used to define surface etch rates.
- 14. The method of claim 2 wherein the said etching is combined with lithographic masking to define surface topography for imprinting surface patterns such as optical gratings and optical phase modulators.
- 15. The method of claim 2 wherein the said etching step is accomplished using an ion beam.
- 16. The method of claim 2 wherein the said etching step is accomplished using an electrical discharge plasma containing fluorine atoms dissociated from a class of fluorine-containing compounds such as NF3, CF4 or SF6.
- 17. The method of claim 2 wherein the said etching step is accomplished using an electrical discharge plasma containing chlorine atoms dissociated from a class of chlorine-containing compounds such as Cl2 or CCl4.
- 18. The method of claim 1 wherein the said optic is cleaned with the most-current best-known cleaning protocol between the advanced finishing and laser conditioning processes. An example of such protocol includes washing thoroughly using distilled deionized water, drying, and cleaning with colloidal alumina or zirconia.
- 19. The method of claim 1 wherein said advanced finishing process comprises the steps of:
application of conventional grinding and polishing to the surface of said optic to attain the near desired surface optical figure, irradiation of the surface of said optic with a CO2 laser to anneal the subsurface damage left on the optics by the said conventional grinding and polishing, application of finishing to the surface of said optic to attain the desired surface optical figure, and application of an etching step to the surface of said optic to remove any contamination arising from the said finishing step.
- 20. The method of claim 1 wherein said optic is one of fused silica, CaF or silicon.
- 21. The method of claim 1 wherein said laser conditioning comprises the steps of:
irradiating said optic with a conditioning laser beam of about 360 nm wavelength or less, irradiating said optic in successive irradiating steps in ramp-like fashion, and irradiating said optic with successive irradiating steps applied in increasingly higher fluences.
- 22. The method of claim 1 wherein said step of irradiating said optic with a conditioning laser beam is conducted with a conditioning laser beam with a wavelength in the range of 360 nm to 150 nm.
- 23. The method of claim 1 wherein said step of irradiating said optic with a conditioning laser beam is conducted with substantially less than the fluence that could cause more than half the density of catastrophic damage sites in an unconditioned optic.
- 24. The method of claim 21, wherein said successive irradiating steps are continued until the density of catastrophic damage on said optic is expected to be reduced by at least a factor of 2.
- 25. The method of claim 1, wherein the laser used to irradiate the said optic at its high fluence design limit is the same as the laser used for conditioning the said optic at low fluences below levels that normally lead to the initiation and catastrophic growth of damage.
- 26. The method of claim 1, wherein the laser used to irradiate the said optic at its high fluence design limit is not the same laser used for conditioning the said optic at low fluences below levels that normally lead to the initiation and catastrophic growth of damage.
- 27. The method of claim 26, wherein the laser used to irradiate the said optic at its high fluence design limit has a wavelength at or near the wavelength of the laser used for conditioning the said optic at low fluences below levels that normally lead to the initiation and catastrophic growth of damage.
- 28. The method of claim 27, wherein the laser used to irradiate the said optic at its high fluence design limit has a pulse length that is shorter than the pulse length of the laser used for conditioning the said optic at low fluences below levels that normally lead to the initiation and catastrophic growth of damage.
- 29. The method of claim 26, wherein the laser used to irradiate the said optic at its high fluence design limit has a pulse length that is longer than the pulse length of the laser used for conditioning the said optic at low fluences below levels that normally lead to the initiation and catastrophic growth of damage.
- 30. The method of claim 1 wherein said step of irradiating said optic at its high fluence design limit is conducted with a laser beam with a wavelength in the range of 360 nm to 150 nm.
- 31. The method of claim 8 wherein said magnetorheological finishing tool is used to imprint surface topographical features onto the optical part for fabricating optical components such as optical gratings and optical phase modulators.
- 32. The method of claim 9 wherein said magnetorheological polishing tool is used to imprint surface topographical features onto the optical part for fabricating optical components such as optical gratings and optical phase modulators.
- 33. A method for reducing the initiation of catastrophic damage on the surface of an optical part, comprising:
the optical part is prepared by an advanced finishing process that minimizes subsurface defects and removes surface contaminants, the optical part is then laser conditioned by exposing it to low fluences below levels that normally lead to the initiation and catastrophic growth of damage, and when the optical part is then irradiated at its high fluence design limit, the concentration of catastrophic damage sites that form on the surface of the optic is greatly reduced.
- 34. The method of claim 33 wherein said advanced finishing process comprises the steps of:
application of conventional grinding and polishing to the surface of the optics to attain the desired, or near desired surface optical figure, application of a finishing step to the surface of the optics to remove the polishing layer and the subsurface damage left on the optics by the said conventional grinding and polishing, and application of an etching step to the surface of the optics to remove any contamination arising from the said finishing step.
- 35. The method of claim 34 wherein the said finishing step, and the said grinding and polishing step, are accomplished with the same tool.
- 36. The method of claim 34 wherein the said conventional grinding is accomplished with a standard optical shop abrasive grinding, such as blanchard or lap grinding, that brings the optics to gross desired dimensional shape.
- 37. The method of claim 34 wherein the said conventional polishing is accomplished by conventional lap polishing using a standard optic shop synthetic-bed or pitch-bed tools containing sequentially smaller sizes of wet abrasive media, such as cerium oxide or zirconium oxide slurries until the desired or near desired optical surface quality and figure are attained.
- 38. The method of claim 34 wherein the said polishing is adjusted to minimize the polishing layer that is composed of redeposited optical material and slurry.
- 39. The method of claim 34 wherein the said polishing is adjusted to minimize the subsurface damage layer that is composed of a network of medial and traversing cracks resulting from high normal stresses imparted by the polishing process.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application No. 60/295,873 filed Jun. 4, 2001, and entitled “Combined Advanced Finishing and UV Laser Conditioning Process for Producing Damage Resistant Optics,” which is incorporated herein by this reference.
Government Interests
[0002] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
Provisional Applications (1)
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Number |
Date |
Country |
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60295873 |
Jun 2001 |
US |