The spectral integrated energy received by a spectrometer's exit slit can be regarded as the slit's response to the superposition of all the shifted monochromatic images of entrance slit
A custom, multireflective entrance slit
plate provides a unique arrangement of nine different slit gaps, ranging from 20 to 100 microns, and three pinholes that you can quickly select using a built-in thumbwheel.
9 comes with a 150 lines/mm grating, 25micron entrance slit
and a non-fluorescing longpass filter that transmits >1000nm.
A fiber-optic bundle carries light from the image plane to the entrance slit
of the spectrometer.
Rays of light entering through the entrance slit
make an angle of [alpha] with the normal to the grating surface (dashed line in Fig la) at the center of the grating.
It was built in a mahogany housing for stability and had an adjustable width entrance slit
, a 20-cm focal length quartz collimating lens, a Comu quartz prism, a 20-cm quartz camera lens and a plate holder for a 3.
Depending on the user-selected configuration of grating options and optical bench entrance slit
size, optical resolution as good as 4.
A second eyepiece "sees" the field of view around the spectrograph's entrance slit
and works with autoguiders for long-exposure imaging.
For a collimated or narrow-angle source, this is not a problem, because the light can be focused onto the entrance slit
, but for tissue, not only is the light source spatially large, it also has a large angular spread.
Briefly, a Ni-coated toroidal mirror collects 20 mrad horizontally and the full vertical extent of the emission from SURF III and focuses the radiation onto an entrance slit
The spectrometer should be able to connect the optical fiber on entrance slit
But to get starlight into the spectrograph's narrow entrance slit
, FUSE must be able to point precisely at a target.