Large diameter optical flats with surface accuracy

25th June 2021

Alex Lynn

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Optical Surfaces has reported on growing demand for larger (350 - 600mm clear aperture) diameters. Working with materials including ClearCeram, Fused Quartz and Zerodur in their thermally stable manufacturing environment - Optical Surfaces has routinely achieved a surface accuracy of up to lambda/20 peak-to-valley and surface roughness of 10 Å rms on reference flats up to 650mm in diameter.

Dr Aris Kouris, Sales Director of Optical Surfaces, commented: "To enable us to quality test reference optical flats up to 650mm in diameter - we developed a 600mm Fizeau interferometer. This is a capability that only a few optical testing and manufacturing centres around the world possess. Housed in an ultra-stable testing environment, this interferometric set-up allows direct qualification of larger reference optical flats by testing them directly over their complete aperture without the need to use time-consuming combination methods.

“This in-house capability increases customer confidence in measurement accuracy and data analysis while minimising potential errors and the time taken to complete the quality testing. We believe this has been a key driver for the increased demand that Optical Surfaces Ltd has received to supply larger diameter reference optical flats".

An optical flat is a precisely polished flat surface, used as a reference against which the flatness of an unknown surface or system may be compared. Reference optical flats are widely used in high precision applications in astronomy, inspecting gauge blocks for wear and accuracy as well as interferometric flatness testing of prisms, filters and optical windows.