Asphere and Free-Form Inspection
Computer-generated holograms (CGHs) extend the surface inspection capabilities of your interferometer for almost any geometry. Diffractive null lenses (DNL) or diffractive Fizeau null lenses (DFNL) are employed for surface inspection with CGHs. This enables the high-precision inspection of aspheres, freeforms, and also aspheric-diffractive optics.
Features and Benefits
Diffractive Null Lenses with Fizeau Reference Surface (DFNL)
DFNLs from DIOPTIC replace the usual combination of transmission sphere and CGH. The time-consuming adjustment of a standard CGH relative to the interferometer is completely eliminated. Our DFNLs are compatible with all Fizeau interferometers – available with bayonet mount in sizes from 4 to 12 inches. DFNLs are preferred for lenses with a low curvature.
DNLs for almost any Surface Geometry
Our DNLs are the ideal reference optics for measuring your aspherical or cylindrical optical surfaces. Testing free-form surfaces is also straightforward. With a maximum measuring range of 220 mm (convex) and more than 1,000 mm (concave), our products can inspect almost any surface geometry with high precision (lambda/10 PV). We manufacture DNLs in standard mounts for all common interferometers.
Simple Adjustment, Fast, and Precise Measurements
The simple measurement setup of our CGHs enables fast and precise testing of optical surfaces. As a DFNL-CGH is attached directly to the Fizeau interferometer, no additional CGH adjustment mechanism is required. Integrated adjustment holograms ensure easy handling. They serve as an alignment aid for precise alignment of the CGH to the interferometer and the test surface to the CGH.
DIOPTIC CGHs
Our CGHs convert the plane wave emitted by the interferometer into an aspherical wavefront that is individually adapted to the test surface. This allows for the detection of even the slightest deviations in the surface shape, as they will appear in the interferogram.
Simple measurement setup for DFNL-CGHs The simple measurement setup when using DFNL-CGHs enables fast and precise testing of aspherical surfaces, cylinders and free-form surfaces. As a DFNL-CGH is attached directly to the Fizeau interferometer, no additional CGH alignment mechanism is required. Auxiliary holograms to align CGHs to the interferometer objective are also not required.
Customized diffractive null lenses (DNL) Surfaces that cannot be inspected with a DFNL due to their strong curvature are usually inspected with a combination of DNL and an interferometer objective (transmission sphere, TS). We manufacture customized diffractive null lenses (DNL) in standard mounts for all common interferometers and promise you short delivery times – including express service.
Specifications
| Parameter | DFNL | DNL |
|---|---|---|
| Surface type | (off-axis) aspheres, Free form surface | (off-axis) aspheres, Free form surface |
| Lens material | Metal, Optical glas (VIS & IR), Plastic optics. (Special coatings on request) | Metal, Optical glas (VIS & IR), Plastic optics. (Special coatings on request) |
| Max. surface diameter | 220 mm (convex) >1000 mm (concave) | 220 mm (convex) >1000 mm (concave) |
| F/# | f/1.5 – 0.7 | f/0.7 (depending on transmission sphere) |
| Accuracy | PV < λ/20 | PV < λ/20 |
| Alignment features | Cat-eye beams | Tilt-alignment retro ring; Focusing and cat-eye beam |
| Fizeau surface | Integrated | Interferometer lens |
Our CGHs with a substrate diameter of up to 220 mm were utilized to test mirrors for the ESA PLATO mission.
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