COS Reference Element for Interferometry

The COS Reference Element is a thick lens with a convex and concave surface, and is the heart of the spherical wave interferometer. Made of Zerodur, a zero expansion glass ceramic material, the reference element's master surface is polished to an accuracy of 1/10 wave or better. A serialized print out from a ZYGO interferomter is supplied with every Reference Element.

The COS reference element for laser interferometry.

The layout of the spherical wave interferometer, with all components identified.

Reference element specifications

Diameter: 27.9mm
R1: 79.3mm convex
R2: 48mm concave
Thickness: 6.8mm
Substrate: Optical quality Zerodur


Reference surface is 1/10 wave or better (usually much better) over an f/3.5 beam. A Zygo interferometer printout is supplied with each serialized Reference Element.

Price: USD $410 + shipping and handling

We accept personal checks (from customers in Canada and the U.S. only) as well as VISA. For VISA transactions add a 3% transaction fee. All payments to be made in USD.

Grin Lens

Also available is the gradient index lens used as the diverging lens in the interferometer. The source, Melles-Griot, has a minimum order policy that can be onerous for the individual telescope maker, so we have purchased a batch and are pleased to provide them to the telescope making community.

Price: USD $45 shipped free with the Reference Element