CoDR Optics Supplement: Overview

1
CoDR Optics SupplementOverview

• Extended Performance, 0.31?m to 1.1?m
• Throughput Estimates (best data)
• Ghosting (simple discussion)
• New issues

-- New full-aperture ADC design (2.5º
prisms) -- Differential distortion -- Effects of
displaced focal surface
2
Extended Performance (0.31--1.1?m)

• Modeled both full- and sub-aperture designs --
  theres virtually no difference between the two
  for dispersion correction.
• Full correction at z60 requires increasing prism
  separation by ?20 over current designs
  (planned).
• Fully-corrected residuals are 0.07" rms and 0.22"
  pk-to-pk.
• Correcting to 0.31?m (vs 0.32) is easy 1.1?m
  most difficult.
• UV PSFs are sim-
• ilar to 0.4?m
• PSFs.

3
Throughput Estimates 95

• Corning provided numbers for UV-grade Fused
  Silica result is about 1 loss for 70mm of glass
  at nearly all wavelengths.
• Sol-gel/MgF2 coatings appear fine (1 loss per
  surface), although performance below 0.4?m is
  still calculated, not measured -- but this
  should simply require reducing thickness of the
  coatings by 20 over the 0.4--1.4?m case.
  (0.4--1.1?m GMOS Sol-gel measured by J.
  Stilburn.)
• LLNL has facilities capable of coating the prisms.

(est. assumes 1 loss per surface)
4
Throughput, contd

• Tuning of coatings will trade off performance in
  the UV vs IR. Do we want to push coatings to
  0.31?m (extinction)? What throughput is needed at
  0.31?m?

5
Ghost Images (Simple Discussion)

• Six surface pairs potentially produce ghosts.
• Ghosts involving non-parallel surfaces (4 pairs)
  will miss the mirror/grating (14.5/7.25
  5.6).
• Parallel surfaces (2 pairs) will produce ghosts
  at a level ?10-4, but these rapidly become
  out-of-focus and much lower contrast.
• Only the inner prism surfaces are likely to be a
  problem, and even there when the ghost level is
  above ?10-6, the ghost image will appear within
  the PSF wings.

6
Differential Distortion
Spot locations

• Spot locations measured at 9 locations and three
  orientations, with prism separation 850mm (full
  correction at Z60), as well as null case.
• For each case, telescope was re-pointed to
  position Spot B at the field center then a
  least-squares fit to translation and rotation
  performed.

G
E
I
A
B
C
D
F
H
7
Differential Distortion
At non-zero angles, rotation is present (up to
0.001)
8
(end presentation)
9
Effects of Displaced Focal Surface

• Telescope must be re-pointed (by ?50", handled by
  guider)
• Displacement of curved focal surface introduces
  focus tilt. (OK for LRIS if tel. focus is
  adjusted)
• It produces dominant differ-ential distortion.
  (tolerable, if pointing adjusted)
• Moves edge of vignetted region around edge of
  LRIS field (potential flat-fielding problem)
• Can we correct with M2??

10
Spot Sizes
Spot locations

• Spot sizes for null-ADC and no ADC are virtually
  identical
• Spot sizes measured at 9 locations and three
  orientations, with prism separation 850mm (full
  correction at Z60)

G
E
I
A
B
C
D
F
H
11
ADC Spot rms-Diameters (")
(calculated at 5000A)
12
ADC Spot 80-Diameters (")
(calculated at 5000A)