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About
the DCL - Optical Design
Assumptions
and Constraints
Design Notes
Optical Design Prescription (PDF)
Schematic
ray diagram of DCL's Offner Optical layout
Computer-Aided Design rendering of Offner layout showing
optical mechanical mounts, mirrors, integrating spheres,
dewar, positioning stages, light source and monochromator.
Scale rendering of non-imaging optical setup, showing
light source, monochromator, filter wheel, integrating
sphere, and dewar; one of several non-imaging setups within
the DCL.
Encircled
Energy curve of the Optical Design
Ensquared
Energy curve of the Optical Design
Spot
diagram of the Optical Design
Assumptions
and Constraints
- Maximum
ensquared energy in a 15 micron pixel, using 500 nm light.
- 61.44
mm x 61.44 mm output image size (4096 15 micron pixels).
- System
housed on a 4'x6' table.
- 3
or fewer powered mirrors for simplicity.
- Maximum
12" diameter mirrors for COTS mounts.
- 2"
clearance outside of clear aperture for COTS mounts.
Design
Notes
The
best choice for achieving this field size, and to have sufficient
aperture for a small diffraction spot, is a modified Offner,
3 mirror system. The unmodified system is corrected for all
third-order aberrations (spherical, coma, astigmatism, field
curvature, and distortion). A few modifications are made to
introduce some third-order aberration in order to compensate
for the dominant residual fifth-order astigmatism.
After
satisfying the field size requirement and other constraints,
the f/number has been adjusted to optimize the ensquared energy.
At slower f/numbers, the system is diffraction limited, but
the diffraction point spread function is large. At faster
f/numbers, the point spread function is dominated by geometrical
aberrations. The optimal speed for this set of constraints
is f/9. The ensquared energy achieved is 86.3% in a 15 micron
pixel, averaged over the field. The center of the field sees
slightly better performance 88.2%.
The
other typical performance indicators are:
- The
geometrical rms spot radius: 2.9 microns average, 1.9 microns
in the field center (these numbers should be rss-ed with
the diffraction spot size of 1.22*f/9*500 nm).
- The
rms wavefront error: 0.044 microns average, .028 microns
in the center.
- The
Strehl ratio at 500 nm: 0.73 average, 0.88 in the center
(0.8 is diffraction limited).
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