Optical Fabrication

Optical Fabrication

REO has a world-renowned capability for optical fabrication and polishing an extensive range of materials and geometries to the industry’s highest level of performance and quality. Utilizing a range of processes including spindle polishing, CNC polishing, diamond turning and continuous polishing, REO has the expertise to meet an exceptional range of fabrication challenges. 

Superpolishing

Illustration to the left illustrates the polish levels via optical profilometer and Nomarski microscope of actual superpolished surfaces.  Measurement were made via REO metrology equipment which allows us to produce some of the smoothest surfaces in the world using proprietary materials and processes developed through years of research and development.  “Superpolishing” refers to processes that are designed to produce surfaces featuring exceptionally low scattering of light in the UV to IR wavelength ranges, often lower than 1ppm. In terms of surface roughness, this typically means significantly less than 1A rms, integrated over spatial scales from approximately 1 micron to 100 microns. Superpolished surfaces may be flat or spherical with a radius of curvature as short as 20mm.

Superpolished surfaces are generally characterized using optical profilometry techniques which are sensitive across the applicable spatial scale. Other techniques such as atomic force microscopy and stylus profilometry may also be used but generally perform best outside of the spatial range generally relating to optical scatter. When coated with a high reflector, the total loss of a surface may be measured with high sensitivity using a cavity ring down technique.

Superpolishing does not relate directly to surface quality, which typically refers to the control of localized defects, such as scratches, digs, coating defects, and certain types of contamination. However, the techniques used to achieve a superpolished surface generally also produce a surface of high surface quality, or low defect levels.

REO produces surfaces with less than 0.3A rms surface roughness over the 1um to 100um spatial range in a number of optically important materials such as fused silica, zerodur, and BK7 glass. Mirrors comprised of such surfaces and IBS high reflecting coatings can achieve total optical scatter levels of significantly less than 1ppm and total loss values less than just a few ppm in the visible and near infrared.

Spherical polishing

REO polishes high performance spherical surfaces using both batch spindle polishing and CNC polishing techniques. Spindle polishing may be used to achieve the highest possible surface roughness, figure accuracy, and surface quality and is suitable for batches of smaller parts – for example up to 38 parts of 25mm diameter may be processed together. CNC polishing provides more efficient polishing of individual optics, and so is suitable for smaller batches and steeper radii of curvature.

 

 

Flat Polishing

REO uses techniques such as continuous polishing and double-side polishing to produce optical surfaces of exceptional flatness. Double-side polishing is used to efficiently produce plane-parallel surfaces of up to 250mm diameter with typical flatness levels of approximately 20nm rms per cm of diameter. Continuous polishing consists of holding parts in a ring-lap configuration typically on a table made of pitch and is used to achieve much higher flatness levels, approximately 3nm rms per cm of diameter, on parts up to 250mm diameter. 

 

 

Diamond Turning

Single Point Diamond Turning is a technique for producing optical quality surfaces using a lathe configuration with a diamond-tipped tool. A primary advantage of this technique is the ability to produce complex aspheric surfaces highly efficiently. It is generally suited to metals and softer crystalline and amorphous optical materials such as ZnS, ZnSe, Ge, Si, and CaF2. The technique can be used to produce rotationally symmetric and off-axis aspheric optics, diffractive optics, and even non-rotationally symmetric optics such as cylinders. 

REO can produce optics up to 200mm using diamond turning, with a departure from best-fit-sphere of up to 1mm, and surface roughness per material as specified in the table below.

Material RMS Surface Roughness Å
CaF2 50
Si 50
Ge 20
ZnSe 40
ZnS 40
Al 35
Cu 20

Metal components can be produced in sizes up to 12 inches (300 mm), with virtually any aspheric profile, including both rotationally and non-rotationally symmetric (e.g. cylindrically aspheric and toroidal) curves, as well as off-axis parabolas . 

  • Up to 250 mm diameter  
  • Figure accuracy: ¼ wave
  • Surface quality 20-20
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