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James Webb Space Telescope
NIRCam At a Glance

Schematic of NIRCAM coronagraphic design

NIRCam consists of an imaging assembly within an enclosure that is mounted in the ISIM. The imaging assembly consists of two fully redundant, identical optical trains mounted on two beryllium benches.

The incoming light initially reflects off the pick-off mirror. Subsequently it passes through the collimator and the dichroic, which is used to split the light into the short (0.6-2.3µm) and long (2.4-5.0µm) wavelength light paths. Each of these two beams then passes through a pupil wheel and filter wheel combination, each beam having its own separate pupil and filter wheel. After this, the light passes through the camera corrector optics and is imaged (after reflecting off a fold flat in the short wavelength beam) onto the focal plane arrays (FPAs).

The FPAs are 2048x2048 format sensor chip assemblies (SCAs). The sensitive area of an SCA is 2040x2040 pixels with a 4 pixel wide border of references pixels along all edges. These pixels are used for tracking bias drifts during exposure. Simultaneously the pixels give Nyquist sampling of the PSF at wavelengths of 2.0 μm and 4.0 μm for Long wavelength(LW) and Short wavelength(SW) channels respectively. The pixel scale for SW channel is 0.0317"/pixel and that of LW channel is 0.0648"/pixel.

NIRCam has three imaging categories: survey mode, small source mode, and coronagraphic mode. In addition, the medium-resolution grisms in the long-wave channel can be used for spectroscopy. Survey and small source modes differ only in the area of sky to be observed and hence many operations will be common between these two modes.

NIRCam will also be used for wavefront sensing to assure perfect alignment and shape of the different primary mirror segments so that their wavefronts match properly.

For a quick look at NIRCam facts see NIRCam Cheat Sheet.

NIRCam Imaging Properties:

Wavelength range (µm)0.6 to 2.3
2.4 to 5
Nyquist λ (µm)2/4
Pixel Format40962 (short λ)
20482(long λ)
Pixel Scale0.032″ (short λ)
0.065″ (long λ)
Field (arc min)2.2 x 2.2 (one module)
Spectral Resolution4,10,100

NIRCam Filters:

Short Wavelength FilterLong Wavelength Filter