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Shape accuracy up to λ / 100 @ 632.8 nm |
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Individual certification including interferograms and topographich maps for each mirror |
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Surface micro-roughness as low as 0.4 nm, rms |
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Plane, Spherical, Cylindrical, Toroidal, Ellipsoidal, Paraboloid, Hyperboloid, Free Form available |
Synchrotron radiation is a high-performance instrument for
many kinds of science and industry applications these days. Due
to extremely small wavelengths and ultra-high vacuum chambers
Synchrotron Radiation equipment brings the research scale to
atomic level, therefore the requirements for optical components
are very high.
It is agreed that the quality of grazing incident optics is defined
by surface figure error. This term describes the maximum (PV)
or average (RMS) deviation of the actual form from the ideal
surface. Since the quality of the focus for grazing incident optics
is primarily determined by slope distribution on the surface, it is
more convenient to use the RMS Slope error to specify the surface
form accuracy. Typical slope error values range from 0.5 arcsec/
rms (for flat surfaces) up to 1 arcsec/rms (aspherical surfaces).
Typical surface geometry of synchrotron mirrors:
• Flat - best slope error is reached.
• Sphere, Cylinder - very good slope error.
• Toroids, elliptic/parabolic cylinder, elliptical toroid - good slope error.
• Ellipsoid (rotary), paraboloid, hyperboloid, Free-form Surface - good slope error.
Manufacturing techniques
There are two techniques for SR Mirrors: Direct Manufacturing
and Replication by negative master form. The direct manufacturing
process generally includes the following steps:
1. Grinding the pre-manufacturing substrates and optical surface geometry.
2. Etching to reduce stress and sub-surface damages.
3. Lapping to set a good thermal contact at the side faces and to optimize the optical surface for next steps.
4. Several levels of polishing to correct and smoothen the surface shape.
For achieving the desired quality a very close interaction between
metrology and polishing is required. Depending on the mirror
type, geometry and required accuracy, fine correction of residual
errors is performed by:
• Conventional polishing. for Plane & Spherical mirrors, rms-Roughness: 2 nm ; 0.5 nm with Magnetorheological finishing.
• Computer controlled fine-correction polishing - tool for figuring aspherical surfaces. Slope errors 0.5-1 arcsec.
• Ion Beam Figuring - highest precision tool for figuring optical surfaces of any form (slope errors <0.1 arcsec)
• Metal Mirrors can also be performed by Diamond Turning methods and Replication Technique.
Test documentation
A complete report including all data of performed measurements
as described before is established for each optical piece. Test
documents are delivered together with optical pieces.
| Typical mirrors substrate materials |
For low SR flux:
• Zerodur, Astrositall (Sitall CO-115M)
• Fused Silica
• ULE
• Glasses (Pyrex, BK7, ...) |
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For high SR flux:
• Silicon (single crystal)
• Silicon Carbide (CVD)
• Cu with electroless Ni layer
• Al with electroless Ni layer |
Coatings
Commonly used coating materials: Au, Pt, Rh, Ni, Pd, Al, Si, C,
Ru, SiO2, Al/MgF2. In some cases (e.g. Ru) a thin Cr binding layer
(0.4 nm) is necessary for reducing stress and also for keeping the
micro roughness performance. Standa offers the "Special EUV
HR" (EUV) for wavelengths < 50 nm. Nominal Reflection for
different metallic coatings at AOI = 75 degree for EUV mirrors
(Theoretical, for nonpolarized ):
| Platinum | Gold Standard EUV (Au_40 nm / Cr_binder) | Nickel
| | R~ 55 - 58 % @ 200 nm - 65 nm | R ~ 55 - 58 % @ 200 nm - 65 nm | R~ 60 - 68 % @ 200 nm - 120 nm |
| R~ 60 - 69 % @ 65 nm - 27 nm | R ~ 55 - 65 % @ 65 nm - 25 nm | R~ 56 - 60 % @ 120 nm - 40 nm |
| R~ 55 - 60 % @ 27 nm - 22 nm | | R~ 60 - 70 % @ 41 nm - 30 nm |
| R ~ 60 - 65 % @ 22 nm - 12 nm | R~ 61 - 70 % @ 25 nm - 15 nm | R~ 30 - 60 % @ 30 nm - 20 nm |
| R ~ 50 - 55 % @ 12 nm - 10 nm | R~ 70 - 71 % @ 15 nm - 9 nm | R ~ 30 - 40 % @ 20 nm - 16 nm |
Reflectivity at 1 Angstrom and energy bandpath at the critical
angle for Au, Be and C coatings acting as a high energy cut-off.
Packaging
Each item is packaged in its own protective container. The
container is the membrane box, and is designed to prevent dust,
contamination and contact of any part of clear aperture. The
packaging of each optic will clearly identify its serial number.
Packing and Delivery
Packing for shipment will insure that each
optic is insulated from severe shock and rough
handling. Each optic will be delivered with
its own documents: optical test report and
conformance certificates.
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