7 August 2014 Slit device for FOCCoS-PFS-Subaru
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The Fiber Optical Cable and Connector System, ”FOCCoS”, subsystem of the Prime Focus Spectrograph, “PFS”, for Subaru telescope, is responsible to feed four spectrographs with a set of optical fibers cables. The light injection for each spectrograph is assured by a convex curved slit with a linear array of 616 optical fibers. In this paper we present a design of a slit that ensures the right direction of the fibers by using masks of micro holes. This kind of mask is made by a technique called electroforming, which is able to produce a nickel plate with holes in a linear sequence. The precision error is around 1-μm in the diameter and 1-μm in the positions of the holes. This nickel plate may be produced with a thickness between 50 and 200 microns, so it may be very flexible. This flexibility allows the mask to be bent into the shape necessary for a curved slit. The concept requires two masks, which we call Front Mask, and Rear Mask, separated by a gap that defines the thickness of the slit. The pitch and the diameter of the holes define the linear geometry of the slit; the curvature of each mask defines the angular geometry of the slit. Obviously, this assembly must be mounted inside a structure rigid and strong enough to be supported inside the spectrograph. This structure must have a CTE optimized to avoid displacement of the fibers or increased FRD of the fibers when the device is submitted to temperatures around 3 degrees Celsius, the temperature of operation of the spectrograph. We have produced two models. Both are mounted inside a very compact Invar case, and both have their front surfaces covered by a dark composite, to reduce stray light. Furthermore, we have conducted experiments with two different internal structures to minimize effects caused by temperature gradients. This concept has several advantages relative to a design based on Vgrooves, which is the classical option. It is much easier and quicker to assemble, much cheaper, more accurate, easier to adjust; and it also offers the possibility of making a device much more strong, robust and completely miniaturized.
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Antonio Cesar de Oliveira, Antonio Cesar de Oliveira, James E. Gunn, James E. Gunn, Ligia Souza de Oliveira, Ligia Souza de Oliveira, Marcio Vital de Arruda, Marcio Vital de Arruda, Lucas Souza Marrara, Lucas Souza Marrara, Leandro Henrique dos Santos, Leandro Henrique dos Santos, Décio Ferreira, Décio Ferreira, Jesulino Bispo dos Santos, Jesulino Bispo dos Santos, Josimar Aparecido Rosa, Josimar Aparecido Rosa, Flavio Felipe Ribeiro, Flavio Felipe Ribeiro, Rodrigo de Paiva Vilaça, Rodrigo de Paiva Vilaça, Orlando Verducci, Orlando Verducci, Laerte Sodré, Laerte Sodré, Claudia Mendes Oliveira, Claudia Mendes Oliveira, "Slit device for FOCCoS-PFS-Subaru", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91514D (7 August 2014); doi: 10.1117/12.2056400; https://doi.org/10.1117/12.2056400

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