Cryogenic system for optical characterization at low temperature

An experimental apparatus for optical measurements at cryogenic temperature has been set-up, using an Oxford static cryostat equipped with optical fibres. On line transmittance and reflectance measurements can be carried out, under vacuum, during the sample temperature variation. Depending on the required minimum temperature, either nitrogen or helium liquid coolant are used and the thermal cycling can be performed in the range 30-300K. The temperature range depends on the specific use of the optical component and laboratory tests are useful to define the component lifetime and its resistance to requirement. The behaviour of several optical coatings at cryogenic temperature has been investigated as far as their optical and mechanical properties are concerned. A set of thin-film coatings (mirrors, filters and single-layer materials) widely used for aerospace instrumentation, have been analyzed in the ultraviolet-visible-near infrared spectrum. The results on their performance after different thermal cycles are reported.