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United States Patent  [ii] Patent Number: 4,915,463
Barbee, Jr.  Date of Patent: Apr. 10, 1990
 MULTILAYER DIFFRACTION GRATING
 Inventor: Troy W. Barbee, Jr., Palo Alto, Calif.
 Assignee: The United States of America as represented by the Department of Energy, Washington, D.C.
 Appl. No.: 259,564
 Filed: Oct 18,1988
 Int. CI.* G02B 5/18
 U.S. Q 350/1.1; 350/1.7;
350/162.19; 350/162.22; 350/162.23
 Field of Search 350/1.1, 1.6, 1.7, 162.11,
350/162.17,162.19,162.22,162.23,162.24, 320, 321; 428/570; 164/14, 72, 75
 References Cited
U.S. PATENT DOCUMENTS
2,688,094 8/1954 Dumond 250/53
3,688,109 8/1972 Gamble 250/51.5
3,887,261 6/1975 Spiller 350/1
3,980,883 9/1976 Franks 50/272
4,101,200 7/1978 Daxinger 350/166
4,313,648 2/1982 Yano et al 350/166
4,576,439 3/1986 Gale et al 350/162.23
4,675,889 6/1987 Wood et al 378/84
4,693,933 9/1987 Keem et al 428/333
Vidal et al., SPIE, vol. 563, pp. 142 to 149, (1985). Ceglio et al., SPIE, vol. 563, pp. 360 to 366, (1985). Ciarlo et al., SPIE, vol. 688, pp. 163 to 170 (1986). Barbee, Jr., Opt. Eng. 25, pp. 898 to 915, (1986).
Barbee, Jr., Appl. Phys. Lett. 50(25), pp. 1841 to 1843, (1987).
Cartwright, JOSA 21, pp. 785 to 791, (1931). Barbee, Jr., Springer Series in Optical Sciences, vol. 43, pp. 144 to 162, (1984).
Barbee, Jr., AIP Conference Proceedings, No. 75, pp. 131 to 145 (1981).
Keski—Kuha, R., Applied Optics, vol. 23, No. 20, Oct. 15, 1984, pp. 3534-3537.
Primary Examiner—Bruce Y. Arnold
Assistant Examiner—Thong Nguyen
Attorney, Agent, or Firm—Gary C. Roth; L. E.
Carnahan; William R. Moser
This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages.
6 Claims, 2 Drawing Sheets
MULTILAYER DIFFRACTION GRATING
The U.S. Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the 5 U.S. Department of Energy and the University of California for the operation of the Lawrence Livermore National Laboratory.
BACKGROUND TO THE INVENTION 1Q
The invention described herein relates generally to diffraction gratings, and more particularly to X-ray to VUV reflection diffraction gratings.
A diffraction grating may be very broadly defined as any arrangement which imposes on an incident wave a 15 periodic variation of amplitude or phase, or both. See the standard text "Principles of Optics, Third Edition", by Max Born and Emil Wolf, Pergamon Press (1965), which is incorporated by reference herein. There are many different kinds of diffraction gratings. Any struc- 20 ture which is periodic in space will serve as a diffraction grating. A very well known type of grating is the transmission diffraction grating, made by ruling equally spaced lines through a silver film that is deposited upon a transparent glass plate. As light passes through this 25 grating, it is diffracted by the narrow slits, usually of equal width and separated by equal distances, in the opaque silver film.
A reflection diffraction grating is produced by ruling a multitude of fine, parallel, equidistant grooves, by 30 means of a diamond point driven by a ruling machine, upon a plate of polished speculum metal. Speculum metal is a hard and brittle alloy of copper and tin, that is capable of taking a brilliant polish, and that is commonly used for making reflectors. If light is incident 35 upon the grating at any angle with respect to the normal, light will be diffracted from the surface of the grating at all angles. A non-spectral, central image is emitted from the grating in the direction of regular reflection, where the angle of incidence is equal to the 40 angle of diffraction. Two series of spectral images, of increasing order, are laterally disposed on either side of the central, zero order image. The dispersion, or separation, of the wavelengths within a diffracted spectrum, increases in proportion to the order of the .spectrum. 45 The shape of the grooves of the grating determines the direction into which the diffracted light will be predominantly thrown. For example, if one face of the grooves is flat, a maximum of energy will be cast into the direction which makes an angle with this face which is equal 50 to the angle made by the incident light with this face. This technique is called blazing, and the spectral order that lies in the blazed direction will be intense.
Synthetic structures, known as multilayers and consisting of alternating layers of high and low atomic 55 number elements, are described in "Multilayers for X-ray Optics", Opt. Eng. 25, pages 898 to 915 (1986), by Troy W. Barbee, Jr. A molybdenum-silicon multilayer monochrometer for use in the extreme ultraviolet, is described by Troy W. Barbee, Jr. et al in Appl. Phys. 60 Lett. 50 (25), pages 1841 to 1843 (1987).
Keski-Kuha, in Applied Optics 23, 3534 (1984), discloses the potential use of layered synthetic microstructures as coatings on diffraction gratings to enhance normal incidence reflection efficiencies. An actual 5000 65 line per millimeter plane holographic grating was produced that was first coated with iridium, and then with a five layered iridium-silicon layered synthetic micro
structure. At 304 Angstroms, the first order efficiency of the grating was enhanced by approximately the factor three. At longer wavelengths the efficiency was reduced.
Vidal et al, in SPIE Vol. 563, 142 (1985) profess to develop a formalism for rigorously computing the efficiency of multilayer coated gratings.
Ceglio et al, in SPIE Vol. 563, 360 (1985) discuss a concept for output coupling from an X-ray laser cavity, wherein a diffraction pattern is lithographically produced on or in a multilayer structure. It is suggested that the pattern may provide periodic or aperiodic amplitude or phase modulation of mirror reflection, with reflected X-rays diffracted into multiple orders. Note particularly FIG. 4(c).
Ciarlo et al, in SPIE Vol. 688, 163 (1986), disclose the use of anisotropic etching to fabricate diffraction gratings on silicon wafers for use as substrates for layered synthetic multilayers. Work on the fabrication of blazed gratings is reported.
Franks in U.S. Pat. No. 3,980,883 issued Sept. 14, 1976 discloses an X-ray diffraction grating in which the grooves are uniformly spaced but of varying depth, to thereby reduce the variation of efficiency of the grating in the region of the wavelength of maximum efficiency. The maximum efficiency of the grating is lowered. To function, X-rays must impinge on this phase grating at extremely small angles of grazing incidence.
Keem et al in U.S. Pat. No. 4,693,933 issued Sept. 15, 1987 teach X-ray dispersive and reflective structures that comprise alternating layers of metallic and nonmetallic materials, with the potential of the layers interacting controlled by utilizing an interfacial buffer layer between the layers.
Wood et al in U.S. Pat. No. 4,675,889 issued June 23, 1987 discuss X-ray dispersive structures, comprised of layer sets formed on one another, which reflect two or more wavelengths at the same or different angles.
Yano et al in U.S. Pat. No. 4,313,648 issued Feb. 2, 1982 disclose a patterned multi-layer structure for a stripe filter used for a photoelectric pickup tube. The multi-layer optical filter is patterned by reactive sputter etching into a stripe pattern.
Spiller in U.S. Pat. No. 3,887,261 issued June 3, 1975 teaches a reflective structure for optical waves that comprises an array of alternate layers of high and low absorbing elements, with the layers coated on top of each other.
Gamble in U.S. Pat. No. 3,688,109 issued Aug. 29, 1972 discusses the use of structurally layered heavy metal chalcogenides as diffraction grating crystals in X-ray optical assemblies.
Daxinger in U.S. Pat. No. 4,101,200 issued July 18, 1978 discloses a light transmitting coating comprised of alternating metallic and non-metallic layers.
Gale et al in U.S. Pat. No. 4,576,439 issued Mar. 18, 1986 teach an improved authenticating device wherein a reflective and diffractive coating layer is situated between the substrate and overcoat layers of the device. The coating layer is divided into a set of small and slightly separated regions, thereby allowing a direct bond of the overcoat layer to the substrate layer within the separation areas.
Dumond in U.S. Pat. No. 2,688,094 issued Aug. 31, 1954 discloses a point focusing X-ray monochromator for low angle X-ray diffraction, that utilizes two crystal reflecting surfaces.