Method for fabricating multi-layer optical films

Abstract

A method for fabricating multiple layer interference optical films by ion beam sputtering, said films being used for mirrors in a ring laser apparatus. An ion beam strikes a target material obliquely, dislodging molecules of the target so that they can be deposited on a surface serving as a base for a multiple layer interference coating. The thickness of the coating is monitored so that the proper thickness of a given layer can be optimized to obtain the type of reflectance desired for a given light wave length. The surface to be coated is rotated during the deposition of the layer of target material. A stack of layers of alternating indices of refraction comprises the optical interference film. The coating process occurs inside of a vacuum chamber where the partial pressures of the gases are carefully controlled to insure the proper ion beam intensity and optimum stoichiometry of the deposited optical films. Prior to beginning the deposition of optical films, the ceramic substrate comprising the mirror base is bombarded by the ion beam at an oblique angle to remove surface anomalies and clean it.

What is claimed is: 
     
       1. A method of fabricating multiple layer optical films.Iadd., said multiple layer optical films comprising optical layers having different indices of refraction .Iaddend.comprising: bombarding targets obliquely with an ion beam .Iadd.produced by or derived from a Kaufman-type ion beam source .Iaddend.in a vacuum chamber to sputter deposit a plurality of optical film layers on a base;   controlling the atmosphere inside .[.of.]. the vacuum chamber to provide sufficient gas to sustain the ion beam and the proper amount of oxygen to accomplish proper stoichiometry of the thin films; and   depositing multiple layers of different materials on said base by varying the targets being bombarded by the ion beam; and   continuously rotating said base during the deposition of said multiple optical layers. .[.2. The method described in claim 1 wherein said multiple layer films comprise optical layers having different indices of   
     
     
        refraction..]. 3. The method described in claim 1 further comprising bombarding said base obliquely with an ion beam prior to bombarding said 
     
     
        targets to clean said base and to remove surface anomalies. 4. The method described in claim 1 wherein optical layers with indices of refraction greater than 2.0 and optical layers with indices of refraction less than 
     
     
        1.5 are deposited in alternating layers. 5. The method described in claim 4 wherein said optical layers with indices of refraction greater than 2.0 
     
     
        are titanium dioxide. 6. The method described in claim 4 wherein said optical layers with indices of refraction less than 1.5 are silicon 
     
     
        dioxide. 7. The method described in claim 4 wherein said alternating 
     
     
        layers are quarter wave layers. 8. The method described in claim 1 wherein the targets being bombarded by the ion beam are cooled to prevent 
     
     
        excessive heat build-up and control sputtering rate. 9. The method described in claim 1 wherein said base is a low expansion ceramic substrate. .Iadd.10. The method described in claim 1 wherein said base and said multiple layer optical films form a mirror. .Iaddend. .Iadd.11. The method of claim 10 wherein said mirror is a ring laser gyroscope mirror. .Iaddend. .Iadd.12. The method of claim 11 wherein said ring laser gyroscope mirror has alternating layers of silicon dioxide and titanium dioxide. .Iaddend. .Iadd.13. The method of claim 10 wherein said mirror is a ring laser gyroscope mirror, and said method further comprises controlling the method parameters so that each of said optical films contains reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser mirrors, and is free of voids. .Iaddend. .Iadd.14. The method described in claim 1 wherein said base and said multiple layer optical film form a quarter wave stack mirror for use with a laser, said mirror having at least two optical layers with 
     
     
        substantially different indices of refraction. .Iaddend. .Iadd.15.  The method of claim 14 wherein said mirror is a ring laser gyroscope mirror. .Iaddend. .Iadd.16. The method of claim 15 wherein said ring laser gyroscope mirror has alternating layers of silicon dioxide and titanium dioxide. .Iaddend. .Iadd.17. The method of claim 14 wherein said mirror is a ring laser gyroscope mirror, and wherein said method further comprises controlling the method parameters so that each of said optical films has reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser mirrors, and is free of voids. .Iaddend. 
     
     
        .Iadd.18.  A method of fabricating multiple layer optical films, said multiple layer optical films comprising at least two optical layers having different indices of refraction, in alternating layers, comprising: bombarding at least two targets comprising materials having different indices of refraction obliquely with an ion beam produced by or derived from Kaufman-type ion beam source in a vacuum chamber to sputter deposit a plurality of optical film layers comprising said materials in alternating layers on a base;   controlling the atmosphere inside of the vacuum chamber to provide sufficient gas to sustain the ion beam and the proper amount of oxygen to accomplish proper stoichiometry of the thin films;   depositing multiple layers of said materials having different indices of refraction on said base by varying the targets being bombarded by the ion beam; and   continuously rotating said base during the deposition of said multiple   
     
     
        optical layers. .Iaddend. .Iadd.19.  The method of claim 1 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 12 or claim 13 further comprising controlling the method parameters so that each of said optical films has a predictable, predetermined density and refractive index, reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser mirrors, is amorphous, and is free of voids. .Iaddend. .Iadd.20. The method of claim 1 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 14 or claim 18 further comprising controlling the method parameters so that each of said optical films has a predictable, predetermined density and refractive index, and reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser mirrors. .Iaddend. .Iadd.21. The method of claim 1 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 14 or claim 18 further comprising controlling the method parameters so that each of said optical films has a predictable, predetermined density and refractive index, reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser 
     
     
        mirrors and is amorphous. .Iaddend. .Iadd.22.  The method of claim 1 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 14 or claim 18 further comprising controlling the method parameters so that each of said optical films has a predictable, predetermined density and refractive index, reduced impurities or surface anomalies of the kind that cause back scatter and absorption in laser mirrors and is free of voids. .Iaddend.