What's it about?
For spherical lenses, 3D in-process metrology is rather simple. Surface form may be tested in reflection using a test plate or a tower interferometer, and the polisher can rapidly assess the progress of the polishing process. For aspheric lenses 3D surface metrology is not easy. It often requires expensive, long lead time holograms or diffractive optical elements, a powerful interferometer and labor intensive setup by a skilled test technician.
All of these factors combine into repeatability errors and suspect results. Looking deeper, there are specific geometries where it may be advantageous to look THROUGH the lens rather than AT the lens. Testing and correcting the aspheric lens as it is used, in transmission, addresses some of the shortcomings of traditional 3D surface metrology.
This presentation will compare and contrast transmission testing versus surface testing for aspheric lenses. It will list specific cases where Optimax Systems chose transmission testing over surface metrology and the reasons for the choice. Additionally it will touch on the techniques and results of this transmission testing.
If form error of a spherical or plano surface is tested in reflection, in-process metrology is rather simple. Using a test plate or a tower interferometer, the polisher can rapidly assess the progress of the polishing process. Change the specification to Transmitted Wavefront Error (TWE) and things become less direct. Transmission testing requires a more specialized setup, and this setup is often in a different location than the polishing equipment...