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24 December 2003 Use of the LIGA process for the production of pyramid wavefront sensors for adaptive optics in astronomy
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Nowadays many groups in the world are developing adaptive optics (AO) systems for the real time correction of the aberrations introduced by the turbolence of the atmosphere in the field of view of the astronomical telescopes. The Shack-Hartmann wavefront sensor has been often used for the detection of the optical aberrations but over the past few years an alternative wavefront sensor with pyramidic shape has being developed. The properties of this sensor have been extensively investigated both theoretically and experimentally (for example in the AO module of the Italian “Telescopio Nazionale Galileo”). Important features of this pyramidal sensor are that it offers the advantage of either variable gain against the wavefront deformation and tunable sampling of the telescope pupil. These features translate into a considerable gain in the limiting magnitude of the reference star when compared to the classical Shack-Hartmann sensor. The manufacturing of single pyramid prototypes has been initially accomplished using the classical figuring and polishing technique, a time consuming procedure. Since the multi-conjugated adaptive optics (MCAO) that are under study, foresee the use of a large number of identical pyramids, it has been investigated and developed an alternative method for the mass production of this optical component. Using a lithography-dedicated beamline already operating at the ELETTRA Synchrotron in Trieste, a manufacturing technique has been implemented that uses a process named LIGA [Lithography, electroplating (German: Galvanik) and molding (German: Abformung)]. With this method is it possible to create a master pyramid made of a polymeric material and having the characteristics requested. The master is then used to create a metallic mold by means of electroforming. In the end the mold is used for the molding of a number of identical pyramids made in a suitable amorphous optical polymer, using the technique of the hot embossing. This technique produce identical copies of the master pyramid, a desirable feature for the MCAO systems, and once the mold has been manufactured, permit a very fast production of large numbers of identical pyramids. In this paper we present the results obtained with this manufacturing process.
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Mauro Ghigo, Emiliano Diolaiti, Frederic Perennes, and Roberto Ragazzoni "Use of the LIGA process for the production of pyramid wavefront sensors for adaptive optics in astronomy", Proc. SPIE 5169, Astronomical Adaptive Optics Systems and Applications, (24 December 2003);


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