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System Description
100
Third, the surface of the Schmidt Cross Disperser has a small waveform on it. This
waveform corrects for the spherical aberrations generated by the camera sphere
mirror. By correcting for these spherical aberrations, the UV channel has excellent
optical throughput (f/2.5) and excellent resolution (0.006 nm at 200 nm). Without
this correction, the system would sacrifice either throughput or resolution.
Fold Flat Mirror
The fold flat mirror deflects the UV light onto the detector. The fold flat mirror size
matches the size of the opening in the Schmidt Cross Disperser. Thus, the mirror
does not impact the optical throughput of the system. The field flattener is a lens
that provides good focus for the entire wavelength range on the UV detector.
Visible Module
The overlapping orders from the echelle grating are passed through the opening in
the Schmidt Cross Disperser to the visible prism. This prism separates the
overlapping orders into discrete orders. A two-dimensional pattern or echellogram
is produced. A compound lens directs the beam onto the solid-state detector for the
visible range.
Segmented-Array Charge-Coupled-Device Detector (SCD)
The detector is a silicon chip with a surface area of 13 mm by 19 mm. On its
surface, the chip has a series of linear subarrays comprised of pixels. The pixels are
photosensitive areas of silicon that have an aspect ratio of approximately eight to
one. This aspect ratio matches the slit geometry of the instrument and ensures
excellent optical throughput. Also, unlike other charge-transfer device detectors,
the pixels have no UV-absorbing polysilicon electrodes over the detector surface.
Thus the quantum efficiency of the SCD is very good throughout the entire
wavelength range of the instrument.
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Troubleshooting
