Optics for X-ray concentrators on board of the Astronomy Satellite SAX

The scientific instrumentation on board of the Italian Satellite for X-ray Astronomy (SAX), foresees X-ray concentrators operating in the energy range 0.1 - 10 KeV with a spatial resolution of the order of 1 arcmin. This paper presents a study for the optics of such concentrators, based on several confocal nested mirrors. To reduce the loss of collecting area due to the thickness of the optics, it is necessary to use very thin mirrors. To achieve this result, still maintaining good optical quality, and to allow the construction of several concentrators at an acceptable cost, the authors propose the use of a replica technique by electroforming the mirrors from masters. The expected characteristics of the double cone geometry mirrors, together with preliminary results obtained with prototypes of electroformed optics are presented