Nickel replicated multilayer optics for soft and hard X-ray telescopes

In this paper we will report on recent progresses obtained in producing astronomical X-ray optics based on multilayer coatings exploiting the replication technique by Ni electroforming of the mirror support shell. It is well known that the use of multilayer reflectors with appropriate structures to be utilized instead of usual high density material (Ni, Au or Ir) monolayer mirrors can allow the extension of focusing techniques also in the hard X-ray energy band (10 - 100 keV). In addition, multilayer mirrors can offer important advantages also for applications in the classical X-ray band (0.1 - 10 keV), e.g. the enhancement of the effective area of a given telescope in a particular energy region of spectroscopical interest. The replication technique by Ni electroforming has already been successfully exploited for making the soft X-ray optics with Au coatings of the Beppo-SAX, JET-X and XMM-Newton space experiments. These telescopes are not only characterized by a large throughput, but they have also shown very good imaging capabilities. The appraoch under investigation from our group for the realization of multilayer grazing incidence telescopes is directly derived, with appropriate modifications, from that experience. We have already been able to fabricate by Ni electroforming replication flat Ni/C multilayer mirrors with a very good X-ray reflectivity. Here we will present some results obtained from the optical and X-ray characterization of conical and double-conical prototype optics recently realized from our group following the same technique. The obtained results are very promising.