Microslices and low cost spectrographs for million element integral field spectroscopy

摘要

We describe a new concept for an integral field unit that allows the collection of a very large number of spectra. We also describe a complementary low cost spectrograph. Both are necessary for the design of integral field spectrographs with huge numbers of spatial elements. These concepts were developed for the Million Element Integral Field Unit and Spectrograph (MEIFUS) that we are proposing for an 8-m and a larger version for an Extremely Large Telescope (ELT, a 30-m telescope). The 8-m version of this spectrograph would give 2.2 million spectra, each 200 pixels long, covering a field of view of 5.2' x 5.2'. The ELT version would give 1.5 million spectra, each 600 pixels long, with a field of 2.7' x 3'. The new concept of microslices for integral field units allows us to pack a large number of short spectra tightly on the detector without oversizing the spectrograph. It uses a series of independent cylindrical microlens arrays, as opposed to spherical or "simulated spherical using cylindrical" microlenses. We used the specific characteristics of our instrument, especially the short spectra, to develop a concept of a low cost spectrograph. We show that MEIFUS fills a technological gap between other integral field systems and Fabry-Perot instruments. We believe that integral field spectrographs with such a large number of spatial elements would be too expensive if they were to use fibers, typical slicer systems or typical spectrograph designs.