Unpublished conference/Abstract (Scientific congresses and symposiums)
Long-wave infrared digital holography for the qualification of large space reflectors
Vandenrijt, Jean-François; Thizy, Cédric; Georges, Marc et al.
2012International Conference on Space Optics 2012
 

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Keywords :
digital holography; metrology; infrared; deformation; speckle; fullfield; interferometry
Abstract :
[en] Deformation metrology of complex and large space reflectors is a recurrent problem addressed by ESA. The challenging tasks of on-ground qualification and verification testing are to achieve the required accuracy in the measurement of these reflectors deformation and to verify their performance under simulated space conditions (vacuum, low temperature). A long-wave infrared digital holographic interferometer for the verification and validation of this type of reflector in a space environment is presented. It has been developed to fill the gap between holography/interferometry techniques in the visible wavelengths and methods based on structured light illumination like videogrammetry, stereocorrelation, and fringe/pattern projection. The former provide a good measurement uncertainty but the displacements are often too large to be measured and they require a very stable environment, while the latter provide large measurement range but with higher measurement uncertainty. The new instrument is based on digital holography and uses a CO2 lasers emitting at 10.6 µm combined with a commercial thermographic camera. A diffuser is illuminated by the laser beam, producing a speckle wavefront which is observed after reflection on the reflector surface. This reflected speckle wavefront behaves exactly as if the reflector was a diffusive surface, producing its own speckle, allowing the measurement of its deformation. The advantage of this configuration compared to a classical interferometer working at 10.6 µm, is that it requires no specific optics such as a null lens (in the case of parabola) or expensive illumination/collection optics (in the case of ellipse). The metrological certification of the system was performed in the laboratory by measuring the tilts of a 1.1 meter diameter parabolic reflector. The displacements are measured in parallel with a Doppler effect interferometer and the measurement uncertainty is estimated. The application of the new interferometer to the measurement of an elliptic reflector is also presented. The technique has been certified during a thermal-vacuum test. The deformation of the parabolic reflector is measured for a temperature variation from 288 K down to 113 K. The results are compared to previous results obtained on the same reflector with a high spatial resolution infrared interferometer, also developed at CSL.
Research center :
CSL - Centre Spatial de Liège - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Vandenrijt, Jean-François  ;  Université de Liège - ULiège > CSL (Centre Spatial de Liège)
Thizy, Cédric ;  Université de Liège - ULiège > CSL (Centre Spatial de Liège)
Georges, Marc ;  Université de Liège - ULiège > CSL (Centre Spatial de Liège)
Queeckers, Patrick
Dubois, Franck
Doyle, Dominic
Language :
English
Title :
Long-wave infrared digital holography for the qualification of large space reflectors
Publication date :
09 October 2012
Number of pages :
4
Event name :
International Conference on Space Optics 2012
Event organizer :
CNES and ESA
Event place :
Ajaccio, France
Event date :
October 9th-12th 2012
Audience :
International
Available on ORBi :
since 10 December 2012

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