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ZTF Optics Design. P. Jelinsky 2013-02-01. Optics Outline. Overview of Requirements Trade Studies Conceptual Design Future Work. Requirements Overview. Use the Oschin Schmidt telescope primary and corrector

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Presentation Transcript
optics outline
Optics Outline

ZTF Technical Meeting

  • Overview of Requirements
  • Trade Studies
  • Conceptual Design
  • Future Work
requirements overview
Requirements Overview

ZTF Technical Meeting

  • Use the Oschin Schmidt telescope primary and corrector
  • Illuminate 12 CCD231-C6 e2v detectors (6k x 6k, 15 µm pixels (~ 1 arcsecond))
    • 16 detectors had large vignetting and worse imaging (see next slide)
  • R band average FWHM < 1.1 arcseconds (final, including alignment and manufacturing)
    • Allow 1.0 arcseconds for the optical design
  • G band average FWHM < 1.2 arcseconds (final, including alignment and manufacturing)
    • Allow 1.1 arcseconds for the optical design
  • Use materials that transmit in the U and I band
    • May add these filters later
requirements overview continued
Requirements Overview (continued)

ZTF Technical Meeting

Detector Pattern

(with vignetting)

No Vignetting

10%Vignetting

20%Vignetting

30%Vignetting

initial trade study inputs
Initial Trade Study Inputs

ZTF Technical Meeting

  • Distance from flattener to CCD is >= 2mm
  • Allow distance from Schmidt corrector to mirror to vary
  • Window diameter/thickness <= 14.4 (same as QUEST camera)
    • Safe to have atmospheric pressure across
  • Window is Fused Silica
  • All spherical surfaces
    • Aspheric surfaces did not change performance much
  • Optimize over 5 wavelengths in the g’, r’ bands as below (allowing a focus change).
  • Optimize over 9 field points
  • Merit function is the 2D FWHM (RMS radius * 2.3548)
bandpass definition
Bandpass Definition

ZTF Technical Meeting

initial trade study
Initial Trade Study

ZTF Technical Meeting

  • Initially did not include a filter in the trade study and concentrated only on the R band
    • Filter seemed to always make design worse
  • Quicker to analyze to limit trade space
initial trade study1
Initial Trade Study

ZTF Technical Meeting

  • No designs with flat detectors and vacuum windows met requirements
12 segment focal plane schematic
12 Segment Focal Plane Schematic

ZTF Technical Meeting

Filter

Window

12 flatteners

12 detectors

12 segment focal plane schematic1
12 Segment Focal Plane Schematic

ZTF Technical Meeting

  • Each detector is flat but tilted with respect to the others (see previous slide)
    • 12 chords on focal plane
  • One vacuum window for all detectors (see previous slide)
    • After FEA center thickness fixed at ~22mm
  • Each detector has its own field flattener (see previous slide)
    • Allow field flattener to be decentered and tilted
12 segment telescope schematic
12 Segment Telescope Schematic

ZTF Technical Meeting

  • Corrector and primary are used as built
    • Corrector is moved 31mm farther from primary (then PTF)
  • Dewar is “hidden” behind the filter
    • Obscuration dominated by the filter and its mount

Corrector

Focal Plane

Primary

detector gap
Detector Gap

ZTF Technical Meeting

  • If t is the thickness of the flattener, d is the distance from detector to the flattener, c is the chamfer of the flattener, g is the gap between the flatteners, f is the f/# of the beam, n is the index of refraction of the glass, and s is the spacing between the optical surface of the detectors, then
  • For g = 2mm, c = 1mm, t = 5mm, d=2mm, f=2.5, n = 1.5 then s = 8.2 mm
    • I assumed 8.4 mm in the analysis (closest allowed given e2v packaging)

Field Flattener

Detector Optical

Surface

12 segment focal plane inputs
12 Segment Focal Plane Inputs

ZTF Technical Meeting

  • Distance from flattener to detector > 2mm (smaller preferred)
  • Distance from flattener to window from 3 mm to 110 mm
    • optics prefers larger; obscuration prefers smaller
  • Distance from window to filter from 15 mm to 110 mm
    • optics prefers larger; obscuration prefers smaller
  • Filter, Window, and flatteners are Fused Silica
    • Good transmission in UV and IR
  • Only Optimized G and R band simultaneously (allowing focus change)
  • Optimize over 5 wavelengths in the g’, r’ bands
  • Optimize over 9 field points in each detector
  • Merit function is the average 2D FWHM (RMS radius * 2.3548)
    • Use RMS field map with 50 x 50 points
12 segment focal plane trends
12 Segment Focal Plane Trends

ZTF Technical Meeting

  • Thicker Windows degrade optical performance
    • 22mm center window thickness gives factor of safety of 8 (from FEA analysis)
  • Thicker filter degrades optical performance
  • Flat filter degrades optical performance
  • Larger CCD – flattener spacing degrades optical performance
12 segment trade study
12 Segment Trade Study

ZTF Technical Meeting

  • PTF Corrector Distance = 6075.3 mm; Original Corrector Distance = 6122.4 mm
  • (A) = asphere; (S) = sphere
case xv imaging results 1 quadrant
Case XV Imaging Results (1 Quadrant)

ZTF Technical Meeting

R Band

G Band

  • R Band average FWHM = 0.60 arcseconds; maximum FWHM = 0.88 arcseconds
  • G Band average FWHM = 1.00 arcseconds; maximum FWHM = 1.26 arcseconds

FWHM (arcseconds)

future work
Future Work

ZTF Technical Meeting

  • Complete I and U band results of current system (quick)
  • Complete optical tolerance analysis
    • Budget/split tolerances into telescope and cryostat sections
      • E.g. filter location (part is telescope filter mechanism/ part is cryostat manufacture)
  • Complete manufacturability/cost studies
  • Add guider and its optics to the system
  • Complete vignetting/obscuration analysis
  • Complete ghosting/scattered light analysis
detector layout
Detector Layout

ZTF Technical Meeting

  • Two Detectors layouts have been considered
    • Minimize the gap in each direction (asymmetrical, need 3 detectors in Zemax)
    • Place detectors centers on a square grid (symmetrical, need 2 detectors in Zemax)

Field locations for minimum gap

Field locations for square grid

  • Only the minimize gap has been studied at the moment
    • The square grid version will be a slight modification to the optics
rms zemax settings
RMS Zemax settings

ZTF Technical Meeting

  • RMS field map settings
    • Ray density = 6
    • Data = Spot Radius
    • Wavelength = All
    • Method = Gauss Quad
    • Center field = 5
    • Refer To = Centroid
    • X field size = 0.8655
    • Y field size = 0.8655
    • X field sampling = 50
    • Y field sampling = 50
    • Surface = Image
  • Use the text->Window->Copy clipboard to place the data into excel for analysis