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Large Diameter Reference Optical Flats

Optical Surfaces Ltd, a leading supplier of high precision reference optical flats to leading research establishments and national standards laboratories worldwide, reports on growing demand for larger (350 - 600mm clear aperture) diameters.

A large diameter reference optical flat being quality tested

Image Credit: Optical Surfaces Ltd​​​​​​​​​​​​​​

Working with materials including ClearCeram®, Fused Quartz and Zerodur® in their unique thermally stable manufacturing environment - Optical Surfaces Ltd. is able to routinely achieve 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 Ltd 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.

For further information please visit or contact Optical Surfaces Ltd. on +44-208-668-6126 / [email protected].

Optical Surfaces Ltd has been producing top quality reference optical flats in single and OEM quantities for more than 50 years. The company’s ISO 9001-2015 approved manufacturing workshops and test facilities are deep underground in a series of tunnels excavated in solid chalk where temperature remains constant and vibration is practically non-existent. With such stable conditions testing, particularly with long path lengths, becomes quantifiable and reliable. Working with these natural advantages is a highly skilled team of craftsmen with a commitment to excellence in both product quality and customer service.

** ClearCeram® is a registered trademark of O’Hara & Co. Ltd. and Zerodur® is a registered trademark of Schott AG.


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