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Optical element that reflects and diffracts light
A
grism
(also called a
grating prism
) is a combination of a
prism
and
grating
arranged so that
light
at a chosen central
wavelength
passes straight through. The advantage of this arrangement is that one and the same camera can be used both for imaging (without the grism) and spectroscopy (with the grism) without having to be moved. Grisms are inserted into a camera beam that is already
collimated
. They then create a
dispersed
spectrum
centered on the object's location in the camera's
field of view
.
The
resolution
of a grism is proportional to the
tangent
of the wedge angle of the prism in much the same way as the resolutions of gratings are proportional to the angle between the input and the normal to the grating.
The dispersed wavefront sensing system (as part the
NIRCam
instrument) on the
James Webb Space Telescope
uses grisms.
[1]
The system allows coarse optical path length matching between the different mirror segments.
See also
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edit
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References
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