The Instrument: Optical Design

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The Instrument Optical Design

• Dr. John T. Mariska
• Data Coordination Scientist
• Naval Research Laboratory
• 202-767-2605
• e-mail mariska_at_aspen.nrl.navy.mil

Dr. Charles M. Brown US Instrument
Scientist Naval Research Laboratory 202-767-3578 e
-mail cbrown_at_ssd5.nrl.navy.mil
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EIS Instrument Schematic
Sun
Filter
Primary
Slit
Grating
CCD Long
CCD Short
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EIS Design Optimization Criteria

• Overall Length lt 3 Meters
• Overall Width lt 0.5m
• Telescope Mirror Diameter 150mm
• Plate Scale 1 arc-sec/Pixel Spatial
• 13.5 Micron Pixels
• Two Wavelength Bands of 40 Å Width
• Short Wavelength Centered at 190Å
• Long Wavelength Centered at 270Å
• Two Detectors Cover 40Å Each
• 4200 l/mm Grating-Single Ruling Density
• Half ML Coated for 190Å
• Half ML Coated for 270Å
• Detector Must Clear Input Path (etc.)

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EIS-7Tr Design Heritage

• Trendy Paraboloid Telescope
• Only Two Reflections
• SERTS Toroidal Grating
• J-PEX Laminar Rulings
• EIT and Trace Sectored Multilayer Coatings
• Sumer Primary Mirror Scan Concept

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Transmission of Al Filter
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F/13 Off-Axis Parabola
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Spot Diagrams for 0, 4 arc min
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Summary RMS Blur of Primary
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EIS-7TR Spectrometer Layout
Slit
Grating
270A
190A
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Comparison of Designs - Summary
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EIS-7T Layout
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EIS-7TR Spectrometer Layout270 Å Band
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EIS-7TrSuper-Optimized by Roger Thomas
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EIS-7Tr Spot Diagrams and Histograms
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EIS-7Tr Field of View 190 Å
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EIS-7Tr Spot Diagrams 170 - 210 Å
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EIS-7Tr Spectral and Spatial Resolution Curved
Focal Surface - Short ? Band
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EIS-7Tr Spectral and Spatial Resolution Flat
Focal Surface - Short ? Band
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EIS-7Tr Spot Diagrams 250 - 290 Å
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EIS-7Tr Field of View 270 Å
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EIS-7Tr Spectral and Spatial Resolution Flat
Focal Surface - Long ? Band
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Detector Locations - Summary
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Multilayer Gratings Characterized by NRL
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NRL Experience With Zeiss Holographic Ion-Etched
Laminar Gratings
1Seely, Applied Optics 36, 8206 (1997) 2J-PEX
mission, Ray Cruddace and Mike Kowalski
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AFM Image of a Zeiss Holographic Grating
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Laminar Grating Efficiency Calculation

• Computer Code Accounts for the Multilayer
  Coating
• Thickness and Optical Properties of the Layer
  Materials
• Interdiffusion Layer Thickness and
  Microroughness
• Laminar Groove Pattern 4200 G/mm, Equal Land
  and Groove Widths, Uniform Groove Depth
• EIS7 Optical Model ? 6.388 and ? 8.526
• Optimal Groove Depth Is H (p?/2)/(cos? cos?)
  Where P 1, 3, ...
• H ?/4 for Normal Incidence
• H Varies Slowly With ? and ?
• 58 Å Groove Depth Is Optimum for ? 6.388 and
  ? 232 Å.
• EIS7 LONG Waveband
• 20 Mo/mosi2/si Periods
• 2d 290 Å, Rpk 24 at ? 268 Å
• EIS7 SHORT Waveband
• 20 Mo/mosi2/si Periods
• 2d 210 Å, Rpk 31 at ? 195 Å

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Groove Efficiency

• Groove Efficiency ? Multilayer Grating Efficiency
  / Multilayer Coating Reflectance
• Laminar Grating With 4200 Grooves/mm and
• Equal Land and Groove Widths ? Zero Even-Order
  Groove Efficiency
• Groove Depth h 58 Å ? Zero 0th-Order Groove
  Efficiency at ? ? 4h 232 Å.
• Odd-Order Groove Efficiencies Varies Slowly With
  Wavelength and Angle

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Multilayer Grating Efficiency
Efficiency in the Two Wavebands in Diffraction
Orders 1 - 3
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Draft Specifications for Primary
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Flight Grating Optical Specifications

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Scientific Performance

• Achieving the EIS Scientific Goals Requires an
  Instrument That Can Obtain Sufficient Numbers of
  Detected Photons in a Single 320 s Exposure to
  Characterize Emission Line Profiles of Interest
• To Verify This, We Have
• Modeled the Instrument Throughput
• Simulated the Ability of the Instrument to
  Measure Doppler Shifts and Nonthermal Velocities
  As a Function of Count Rate

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EIS Is a Stigmatic Spectrometer
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EIS Slit and Raster
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Instrument Throughput

• Throughput for the Entire Optical Chain Has Been
  Modeled Using
• Mirror Area 88.4 cm2 (Half of a 15 cm Diameter
  Mirror)
• Grating Groove Efficiency 0.40
• Detector Quantum Efficiency 0.80
• Obscuration by Front Filter Support Structure
  0.80
• Obscuration by Mesh Supporting Front Filter
  0.80
• Wavelength-Dependent Transmission Curves for Two
  Thin Al Filters
• Wavelength-Dependent Multilayer Efficiencies for
  Mirror and Grating Computed by J. Seely
• Slit Width 1 Arcsec
• Solar Spectra Computed Using Chianti Atomic
  Physics Database and Emission Measure Curves for
  Quiet Sun, Active Regions, and Flares

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Active Region Performance
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EIS Quiet Sun Performance
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EIS Flare Performance
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Velocity Resolution

• Estimates of Errors in Velocity Measurements
  Assume
• Dispersion
• Long Wavelength 25.7 km s-1 Per Pixel (0.023 Å)
• Short Wavelength 36.5 km s-1 Per Pixel (0.023 Å)
• Spectral Resolution
• Long Wavelength 11.0 mÅ rms (21.5 fwhm)
• Short Wavelength 10.7 mÅ rms (24.1 fwhm)
• CCD Pixel Size 13.5 Microns
• Nonthermal Velocity 20.0 km s-1
• Formation Temperature of Emission Line 1.5 MK
• Atomic Mass 56
• Rest Wavelength
• Long Wavelength 270.0 Å
• Short Wavelength 190.0 Å

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Long Wavelength Velocity Error Estimates
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Short Wavelength Velocity Error Estimates