IBIS: A New Post-Focus Instrument for Solar Imaging Spectroscopy

A new instrument for solar bi-dimensional spectroscopy, the Interferometric BIdimensional Spectrometer (IBIS), has been successfully installed at the Dunn Solar Telescope of the National Solar Observatory (USA-NM) in June 2003. This instrument is essentially composed of a series of two Fabry-Perot interferometers and a set of narrow-band interference filters, used in a classic mount and in axial-mode. It has been designed to take monochromatic images of the solar surface with high spectral (R ≥ 200 000), spatial ≃ 0.2″), and temporal resolution (several frames s⁻¹). IBIS has a circular field of view, 80″ in diameter and, with suitable interference filters, it can be used in the wavelength range 580 – 860 nm. The wavelength stability of the instrumental profile is very high, the maximum drift in 10 hours amounting to ≃10 m s⁻¹. In this paper the criteria used in the design and the expected instrumental characteristics are described.