OPTICON JRA5 - Smart Optics

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Figure 1:Replication of small optical parts through galvanic-replica technique.

OAPd is involved in the Joint Research Activity number 5 of  of OPTICON handled by the European Community. The aim of JRA5 group concerns principally the development of smart optics for focal plane instrumentation. Smart optics include all miniaturized and movable optical systems to be used in the scientific instrumentation of the new generation ground telescopes.

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Figure 2:Vacuum system for the replication of optical parts with epoxy resins.

 OAPD participates to the design, implementation and metrology of monolithic Image Slicer devices. They are low dimension optics able to separate a light beam with extreme accuracy and then send every portion to a different part of the instrument to be independently analysed. Very shortly, an image slicer, when coupled with a spectrograph, produces the integral (i.e. x, y spatial coordinates plus wavelength ‘coordinate’) spectroscopic analysis of a light source distributed over a spatial area. So the main characteristics of an image slicer is to sample small areas of the focal plane with high light collecting efficiency. After some first trials of slicing mirrors replication with galvanic methods made in cooperation with Media Lario company (see Fig. 1), we concluded during 2006-2007 the project with the following activities:

  • A. Epoxy-resin replication of mirror slices
  • B. Silicon-Carbide PECVD replication of mirror slices
  • C. Optical design of realistic image-slicer assemblies
  • D. Construction of an image-slicer assembly with direct, non replicating, techniques
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Figure 3:Flat SiC optical surface made with PECVD replication technique.

A - A first epoxy-resin deposition system has been assembled at the Asiago Observatory. It allows the mixture in controlled proportions and under stable conditions (pressure and temperature) of the resin components (See Fig. 2). After several experiments we achieved a good knowledge and practice in the modalities to operate the system obtaining resin compounds with the correct composition and completely out-gassed. Replicas for flat surfaces have been already obtained.

B - This activity has been made in close cooperation with SELEX (Galileo Avionica) company in Carsoli. The first attempts to create PECVD depositions of hydrogenated SiC on the challenger mandrel evidenced the problematic concerned with the separation of the replica from the master. As already evidenced in the galvanic replica case the problem is twofold: - Different level of reciprocal penetration between master and replica, - Different thermal expansion coefficient between the two parts (zerodur and SiC or Alluminium and SiC).  

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Figure 4:Slicer mirror prototype made in Stavax Iron.

A study and experiment of a different separation technique that makes use of the coating layer previously deposited on the master (thick gold layer) as a 'sacrificial layer' to be chemically dissolved in order to facilitate the separation has been made. Usually (galvanic replication case) this coating layer is donated from the master to the replica and is used as final reflecting layer. A successful experiment of this technique has been made creating a simple flat SiC surface growth on a silicon wafer (See Fig. 3) C-D - This activity concerned the optical design within the Zemax ambient of a practical image slicing system, its mechanical design (optical slices and support system) and the practical construction by electrical erosion and/or laser cutting technique. A prototype with slices made in Stavax iron has been tentatively assembled (see Fig 4). After polishing of the optical surfaces and reflective coating deposition, it will be tested in an optical bench.

People: F. Bortoletto, L. Contri, E. Giro, L. Lessio, D. Magrin, G. Martorana

Collaboration: INAF OA Merate, ROE Edinburgh, Durham University

Publications: Magrin et al. (2008), SPIE 7018,102

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