Design and construction of a focal plane slicing mirror Demetrio Magrin a , Enrico Giro a , Favio Bortoletto a , Giuseppe Crimi b , Claudio Pernechele c , Raffaele Tomelleri d a INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy b INAF – Osservatorio Astronomico di Brera, sede di Merate, via E. Bianchi 46, 23807 Merate (LC), Italy c INAF – Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54 09012 Capoterra (CA), Italy d Tomelleri Srl – Viale Del Lavoro,12/A, 37069 Villafranca Di Verona, Italy ABSTRACT We describe here the optical design, mechanical project and the manufacturing of a mechanically reconfigurable spherical slicing mirror. We made use of nowadays commonly available mechanical cutting techniques (wire spark- erosion) to obtain single blades (slices) shaped with profile close to the optical sag specification. Blades so constructed are ready to be optically finished with standard optical workshop techniques. We present here the results obtained from metrology made on the first constructive phase of the system before to start the final optical polishing phase. Keywords: slicing mirror, integral field unit, mechanics, optics, metrology. 1. INTRODUCTION The aim of the Integral Field Spectroscopy (IFS) is to provide the spatial and the spectral information over an extended portion of the sky by optical subdivision and multiplexing of the same. The basics of this observation technique and the possibilities for developing conventional IFS have been largely explored and can be divided in three different kinds of approaches following the nature of the optical element used as field sub-divider: • The use of a two-dimensions lenslet array [1][2] • The use of a two-dimensional lenslet array coupled to a fibre-bundle [3] • The use of an image slicing mirror array [4] All three designs are based on a traditional spectrograph where the field of interest of the telescope focal plane is dissected and relayed to spectrograph input slit. In this fashion the slicer can be viewed as a removable optical unit (Integral Field Unit, IFU) realizing a retrofit of a previously available spectrograph. The first two concepts differs basically in the way to multiplex the resulting slicing spectra on the spectrograph final detector allowing different optimizations in terms of detector surface usage, sky sampling and overall throughput. The third concept allows the construction of a full reflective slicing unit or hybrid in that the critical part, the slicer, is reflective and the slit re- imaging optics is refractive. The field of interest is in this case subdivided in one dimension by the reflecting facets composing the slicer, the second spatial dimension is recovered from the natural spectrograph spatial coordinate orthogonal to dispersion. A further differentiation among mirror slicers is between plane and spherical slicer facets, the first case providing easier manufacturing and the second easier optical alignment of facets [5]. The present paper is concerned with the optical design and mechanical construction of spherical mirror-slicers. In the framework of the OPTICON JRA5 activity we experimented the possibility to replicate slicing-mirrors starting from monolithic aluminum and zerodur negative mandrels constructed by diamond-turning machining. Replication has been attempted both with nickel galvanic deposition and SiC plasma enhanced chemical vapor deposition (PECVD) [6]. This technique allows in principle the possibility to produce an high number of similar pieces but at the expense of long experimentation trials in order to minimize the deformations induced on replicas by temperature gradients and electric-field disuniformities on the mandrel surface. The present work is concerned with the Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, edited by Eli Atad-Ettedgui, Dietrich Lemke, Proc. of SPIE Vol. 7018, 701837, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.787550 Proc. of SPIE Vol. 7018 701837-1 2008 SPIE Digital Library -- Subscriber Archive Copy