A wide field (6x6 arcmin2) Rapid Infrared-Visible Multi-Object Spectrometer (RIVMOS) has been designed and is being fabricated at NASA's GSFC as part of the Next Generation Space Telescope (NGST) development and new technology demonstration. The primary goal is to demonstrate that the microshutter arrays, currently being designed for the NGST Near Infrared Spectrometer (NIRSpec) as programmable 2D selection masks, can achieve the optical performance required for faint object imaging and spectroscopy.
We developed an original optical design that includes both reflective and refractive optics. The primary goal of the design was to achieve high imaging quality in both imaging and spectroscopy modes over a very wide spectral range with all spherical surfaces. The required optical performance is achieved for both multi-object spectroscopy and camera imaging over the entire field-of-view. The optical design consists of six optical subsystems including (1) an image relay consisting of a three-mirror anastigmat (TMA), (2) the microshutter assembly, (3) a triplet collimating optic, (4) a grism/filter assembly, (5) a pupil imaging optic, and (6) a five element telecentric camera design.
The all-spherical optical design reduces construction costs and facilitates fabrication of the optical assembly while maintaining an encircled energy of 2 pixels within the FOV for wavelengths between 0.6 and 5.0 microns. Three spectral resolution modes (R = 50, 2000, 4000) will be available for multi-object spectroscopy as well as cross-dispersed echelle spectroscopy at the highest spectral resolution. The low resolution mode will be provided by the direct view prism, whereas silicon grisms will be used for higher resolving power. This design provides an extremely wide spectral range, wide field, very compact, high resolution imager-spectrometer with multi-object capability.