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NIRI properties

NIRI Optical Properties

The optical elements of NIRI (e.g. cameras, filters, grisms and slits) are described in detail on the NIRI pages.

The filter menu is divided into broad- and narrow-band filters, in order of increasing wavelength. For spectroscopy, select the "grism order sorting" filter from the menu, the appropriate grism (disperser) and slit.

The wavelength coverage of the J and L grisms can be shifted bluewards by selection of the blue offset slit (see the NIRI grism page for more details). For computational simplicity, the slit width is assumed to define the spectral resolution (i.e. it is assumed that the source fills the slit for calculating resolution but not for calculating slit throughput).

Note that even though specific capabilities are listed in the ITC, they may not be available in every semester. For the latest information on the delivery of specific narrow band filters, please check the NIRI filter page.



NIRI Detector Properties

Detector bias: the bias is adjustable to provide an increased well depth for high-flux observations such as imaging at thermal wavelengths (3-5um). Even with a deeper well the high background flux typically means that multi-NDR (non-destructive readout) is not possible otherwise the detector will saturate.

The exposure times for 50% of full-well depth on the typical background are given on the NIRI imaging exposure times page.  

Detector read noise: typical single-read and NDR noise characteristics, which vary with the number of non-destructive reads and digital samples, are given on the NIRI science detector page. The ITC currently adopts a fixed value of 13e- for multi-NDR, low-noise observations (typically at wavelengths <2.5um) and 50e- for fast-readout, high-noise observations (>2.5um), which will normally be background noise limited in any case. These values are derived from lab measurements with the science detector.

Dark current: lab characterisation indicates a value of 0.25e-/s at the adopted operating temperature. This may include some internal cryostat background (e.g. a low-level light leak).



Last update August 28, 2000; Phil Puxley