NOVA-ASTRON has delivered a suite of cryogenic astronomical instruments for large ground based telescopes as well as space missions. The instruments include polarimeters, spectrometers, cameras and interferometers, mostly operating at infrared. Several methods have been developed to verify or measure, under cryogenic conditions, the performance of optical components, coatings and complete optical systems.<p> </p>The test and verification setups presented in this paper include wave front error measurements, alignment inspection, spectral measurements, material properties determination and varying gravity orientation capabilities (gravity load vector). The measurement principles are explained, together with the most important error contributions and the achieved accuracies.
The baseline design of the European Extremely Large Telescope features a telescope with a 39-meter-class
primary mirror (M1), consisting of 798 hexagonal segments. A measurement machine design is presented based
on a non-contact single-point scanning technique, capable of measuring the form error of each segment with
nanometer uncertainty, fast, and with low operational costs. The implementation of a tactile precision probe
eliminates the need for the CMM in the earlier segment manufacturing process. Preliminary assessment show
nanometer-level uncertainty after calibration.
Adhesives are widely used in optomechanical structures for bonding optical components to their mounts. The main
advantage of using adhesives is the excellent strength to weight ratio. Adhesive bonding is seen as a desirable joining
technique as it allows for greater flexibility in design. A disadvantage of adhesives however is the limited dimensional
stability and loadability. To design stable optical mounts, accurate prediction of stresses and deformation is therefore
Adhesives show strong temperature and loading history dependent behavior. Viscoelastic material models are needed for
accurate prediction of stresses and strains in bonded joints. However, representative material data for adhesives is
difficult to find.
In this research, an experimental framework is build up to determine relevant mechanical properties of adhesives for
improving stress and deformation prediction. This paper shows the results of the characterization experiments and
modeling techniques. Also the implementation of material models in finite element code is briefly discussed. The
obtained models are used in the mount design in the EUCLID and TROPOMI programs as described in “Ultra stable isostatic
bonded optical mount design for harsh environments, J.A.C.M Pijnenburg et al” (this conference).
Through the years many stable optical mounts have been designed, analyzed and tested at TNO. This paper gives an
overview of the design principles used. Various examples are presented together with verification test results.
The use of adhesives in combination with an iso-static mount design allows mounting of optical components in a limited
volume with limited deformation of the optical surfaces due to thermal and mechanical loads. Relatively large
differences in thermal expansion over large temperature ranges can be overcome using a simple and predictable design at
reasonable costs. Despite adhesives have limited dimensional stability and loadability, stable optical mounts can be
realized when proper design principles are used.