EP0954764A1 - Miroir composite - Google Patents

Miroir composite

Info

Publication number
EP0954764A1
EP0954764A1 EP98900565A EP98900565A EP0954764A1 EP 0954764 A1 EP0954764 A1 EP 0954764A1 EP 98900565 A EP98900565 A EP 98900565A EP 98900565 A EP98900565 A EP 98900565A EP 0954764 A1 EP0954764 A1 EP 0954764A1
Authority
EP
European Patent Office
Prior art keywords
backing layer
micro
composite mirror
binding agent
mirror
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98900565A
Other languages
German (de)
English (en)
Inventor
Jonathon Philip Nunn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UK Secretary of State for Defence
Original Assignee
UK Secretary of State for Defence
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by UK Secretary of State for Defence filed Critical UK Secretary of State for Defence
Publication of EP0954764A1 publication Critical patent/EP0954764A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
    • G02B7/182—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors

Definitions

  • the present invention relates to a composite mirror and in particular to one suitable for use as either a flat precision optic or as a deformable optic of either flat or curved form and which, for example, may be used in high power laser systems.
  • the amount of glass in mirrors of some laser systems can weigh several tens of tonnes and can present severe mounting problems.
  • Such traditional mirrors have a ratio (R) of largest surface dimension to thickness of between 5:1 and 8:1.
  • R ratio
  • any rnirror used in these laser systems must be capable of being finished to provide a surface having an operational variation from flatness, which includes self weight distortion and distortion due to adjusting the mounted mirror, of less man ⁇ /4 where ⁇ is the wavelength of laser light to be reflected.
  • monolithic glass structures, employed as a flat precision optic are typically 400mm square by 55mm thick (R ⁇ 7:l) show self weight distortions of between 0.14 ⁇ m and 1.8 ⁇ m even under the best mounting conditions.
  • Composite mirrors are also known having a reduced weight over monolithic glass mirrors and comprise a reflectively coated sheet, formed from glass or a suitable ceramic material, bonded to a less dense honeycombed backing layer, usually made from a ceramic material in which a plurality of evenly sized and spaced holes have been made, for example by drilling.
  • a problem with the use of such a honeycombed layer is that unless the reflecting surface is made sufficiently thick then, when polished, the reflecting surface exhibits the quilting effect, as with the all glass structures, reflecting the honeycombed backing.
  • the quilting effect may be reduced either by reducing the cross sections of the individual voids or by increasing the thickness of the reflecting surface.
  • both solutions are at the expense of an increased mirror weight and lead to a reduced R value.
  • a composite mirror having a reflective sheet bonded to a backing layer characterised in that the backing layer comprises a multiplicity of inclusions consisting of micro-cellular material and a binding agent adapted to bind the inclusions therein.
  • the syntactic foam material formed by the inclusion/binding agent mixture provides a backing layer in which the void size compared with those of the honeycomb backing is significantly reduced to thereby eliminate quilting. Consequently thinner refecting sheets may be used formed from, for example, glass or ceramic.
  • the micro-cellular materials may be selected to have a lower density than the binding agent, which may for example be a ceramic, a rubber, a plastic or a resin material.
  • the binding agent which may for example be a ceramic, a rubber, a plastic or a resin material.
  • This provides a light weight mirror system having a backing layer with a higher specific stiffness (defined as ⁇ /p where ⁇ is Young's Modulus and p is the density of the backing layer) than a honeycombed structure of the same binding agent. This is due to the presence of material where, in a honeycomb, there would exist a void.
  • the higher specific stiffhes provides a the further advantage in that a smaller ' thickness of backing layer may be employed to support any given thickness of reflective sheet without significant distortions occurring due to twisting as a result of gravity effects.
  • the binding agent with micro-cellular inclusions may be chosen to provide a backing layer with a density less than a glass sheet reflector and with a greater specific stiffness. This would allow a mirror to be made which is lighter and which has a higher specific stiffness than a monolithic glass or a sandwich glass mirror and which has an R of 10: 1 or greater.
  • the composite mirror may be made stiffer by applying a high stiffness material, such as an aluminium sheet, to the face of the backing layer opposite the reflecting surface.
  • a high stiffness material such as an aluminium sheet
  • the inclusions may be formed from so called micro-spheres or from elongate foamed ceramic pellets, for example a prill such as TECPRLL (TM), available from FILTEC Limited, Widnes, Cheshire. These elongate pellets, largely due to their shape, produce a higher specific stiffness backing than using just the micro-spheres in the same binding agent.
  • a combination of micro-spheres and pellets may be employed, the micro-spheres being able to fill voids between the pellets to reduce the free spaces in the binding agent itself and thereby increase its specific stiffness.
  • ceramic is selected as the binding agent the presence of micro- spheres makes it more flowable.
  • the weight percentage of micro-spheres and prill in the ceramic bonding agent is between 2-20 % and 8-15% respectively, particularly between 14-16% and 9-11% and most particularly 14.9% and 9.9% respectively.
  • the coefficient of thermal expansion of the backing layer may be made substantially that of the reflecting sheet by varying the constituent weights and curing conditions in ways clear to a person skilled in the art.
  • the reflecting sheet comprises a polished glass it may be bonded to the backing layer using a glass net (a so called frit) to maintain an adhesive film of substantially uniform thickness, the adhesive being selected to have a curing temperature lower than the distortion temperature of the glass sheet
  • frit a glass net
  • other bonding techniques being common in the art, may be employed.
  • Figure 1 shows a part sectional view of a precision optic mirror according to the present invention.
  • Figure 2 shows a mounting point for use with the mirror of Figure 1 with 2a showing a ceramic insert used in the mounting point and 2b showing the insert and anchor assembly.
  • Figure 3 shows a flat deformable mirror assembly
  • a lightweight precision optic 1 comprises a flat, polished glass sheet 2 bonded to a syntactic ceramic foam backing layer 3 using a glass frit 4 and adhesive 5.
  • the backing layer 3 has a number of mounting points 6 made in it, for example by fo ⁇ ning threaded sockets after the layer 3 has solidified or by setting the mounting points into the layer 3 during its solidification.
  • the layer thickness of the adhesive 5 is controlled by the frit 4 since it is spread over the frit 4 to fill in the spaces between the individual glass strands. Thus the layer thickness is maintained at substantially that of the glass frit 4.
  • the backing layer 3 is formed from a micro-cellular material comprising mixture of micro-spheres and a ceramic prill dispersed in a ceramic binder to form a syntactic foam.
  • the density of this backing layer will have a lower density than one formed from the ceramic binder.
  • the backing layer 3 may comprise:
  • the alumina powder is chosen to have an average grain size of typically between 48 mesh and 50 ⁇ m.
  • the self weight deflection of a 400 mm square by 50 mm thick mirror is 0.05 ⁇ m which is between 3 and 36 times better than the glass monolith.
  • a simple drilled out mounting point may be used in the composite mirror 1 but this is found to have a relatively low pull out force of about 0.8kN.
  • a mounting point as shown in Figures 2 may be used.
  • a removable insert (not shown), for example made of silicone rubber, is cast into a conical ceramic plug 7. On removal of the insert an undercut hole 8 is left in the ceramic plug 7.
  • the required number of such plugs 7 are arranged in the mirror backing layer mould and the backing layer mixture is added which is then freeze cast and fired after drying.
  • the plugs 7 co-fire with and bond into the backing layer
  • An anchor comprising a bolt 9 and retaining spring 10 arrangement is then inserted in the plug 7 as shown in Figure 2b to provide a mounting point with a pull out force of about 2kN.
  • the external mount may be secured directly to the bolt or may be screwed into a female threaded collar 11.
  • a curved rnirror (not shown) may be made using these above described components relatively simply.
  • the backing layer 3 could be moulded in the required shape and the glass reflector 2 heated to its distortion temperature and allowed to slump on to the curved backing layer.
  • the resulting mirror would be much more temperature stable than a conventional curved mirror which has been shaped by pohshing. This is because a curved mirror according to the present invention would have a substantially uniform reflector thickness as compared with a conventional curved mirror where the thickness varies with the curvature so that its thermal properties will vary correspondingly.
  • FIG. 3 This comprises a reflector 13 bonded to a compliant syntactic foam layer 14.
  • Actuators 15 a . ⁇ are positioned within the layer 14, arranged depending on the deformed profile required of the reflector, and pass into a stiff backing plate 16 which will tend to resist deformation caused by movement of the actuators 15aha n .
  • Associated with each actuator 15a.. n are individual drives (not shown) which can be operated to push or pull an activator 15 in order to achieve the required distortion.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Laminated Bodies (AREA)

Abstract

Ce miroir composite (1) comprend une surface réfléchissante (2) fixée sur une couche support en mousse syntactique (3) au moyen d'un adhésif (5). La couche en mousse syntactique (3) comprend une multiplicité d'inclusions consistant en une matière micro-cellulaire, telle qu'un utricule et/ou des microsphères, liés dans un agent de liaison, comme une céramique.
EP98900565A 1997-01-24 1998-01-09 Miroir composite Withdrawn EP0954764A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9701519 1997-01-24
GBGB9701519.2A GB9701519D0 (en) 1997-01-24 1997-01-24 Composite mirror
PCT/GB1998/000069 WO1998033083A1 (fr) 1997-01-24 1998-01-09 Miroir composite

Publications (1)

Publication Number Publication Date
EP0954764A1 true EP0954764A1 (fr) 1999-11-10

Family

ID=10806561

Family Applications (1)

Application Number Title Priority Date Filing Date
EP98900565A Withdrawn EP0954764A1 (fr) 1997-01-24 1998-01-09 Miroir composite

Country Status (5)

Country Link
EP (1) EP0954764A1 (fr)
JP (1) JP2001509279A (fr)
CA (1) CA2277104A1 (fr)
GB (1) GB9701519D0 (fr)
WO (1) WO1998033083A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2849508B1 (fr) * 2002-12-31 2005-02-25 Kevin Saleh Dispositif de type reflecteur optique en matiere polyurethane integrant un dispositif de type barillet

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1581455A (en) * 1977-06-28 1980-12-17 Bfg Glassgroup Mirrors
US4856887A (en) * 1987-04-01 1989-08-15 Hughes Aircraft Company Lightweight silicon carbide mirror

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9833083A1 *

Also Published As

Publication number Publication date
GB9701519D0 (en) 1997-03-12
WO1998033083A1 (fr) 1998-07-30
CA2277104A1 (fr) 1998-07-30
JP2001509279A (ja) 2001-07-10

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