NIRSpec optics: NIRSpec is an all-reflective instrument with a total of 14 mirrors along the light path, and interchangeable filters and disperser options to cover the science wavelength range. The NIRSpec Optics article describes the basic optical path and components.
NIRSpec dispersers and filters: NIRSpec is sensitive to nearly a full decade in wavelength: 0.6–5.3 µm. The NIRSpec optical path contains 2 wheel mechanisms—the filter wheel assembly (FWA) and the grating wheel assembly (GWA)—that provide disperser/filter combinations to cover the NIRSpec wavelength range. The NIRSpec Dispersers and Filters article describes the FWA and GWA components used for spectroscopy.
NIRSpec detectors: NIRSpec uses 2 "long wavelength cutoff" Hawaii-2RG detectors manufactured by Teledyne Imaging Systems to acquire near-infrared spectra in the 0.6–5.3 μm spectral range. The NIRSpec detectors have 2048 × 2048 pixels; the inner 2040 × 2040 pixels are light sensitive.
NIRSpec integral field unit: this NIRSpec observing mode obtains the spectra of a contiguous, extended 3"×3" area on the sky. To achieve this, the IFU uses specialized optics to "slice" the extended spatial region and reformat it into a slit alignment that can be dispersed using the NIRSpec spectrograph optics shared with the multi-object spectroscopy (MOS) and fixed slit (FS) observing modes. This article describes some key characteristics of the NIRSpec IFU.