The thermal sieve: a diffractive baffle that provides thermal isolation of a cryogenic optical system from an ambient temperature collimator

We present the thermal sieve, which is a diffractive baffle that provides thermal isolation between an ambient collimator and a cryogenic optical system being measured. The baffle uses several parallel plates with holes in them. The holes are lined up to allow the collimated light to pass, but the view factor for thermal radiation is greatly reduced. A particular design is shown here that allows less than 0.25 W/m2 thermal transfer and degrades the test wavefront by only 3 nm rms.