Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

Optical

VIEWS: 10 PAGES: 25

									     NICI Optical Design and
     Performance SDN 1007

•   Science derived optical requirements
•   Layout
•   Performance
•   Tolerancing
•   Optical flexure
             Science Derived Optical Requirements
Science Requirement              Optical Requirement
Coronagraphic imaging            Focal plane and pupil masks
                                 Low-scatter reflective optics (minimize number of
                                 components)
                                 Low ghosting design
                                 Pupil imager for mask alignment
                                 12.5mm diameter pupil (larger for mask positioning,
                                 smaller for lower aberrations)
                                 Rotating spider mask
High Strehl images over 1-5μm    High Strehl optics at 1.25μm (>90%)
                                 Adaptive Optics
Spectral difference imaging      Many beamsplitters and filters
                                 Identical optics following split
Coronagraphic photometry         Many broad-band filters (>20)
Low to medium-res spectroscopy   Grism in filter wheel
                                 Slit in focal plane
Astrometry                       Stable positioning
                                 Characterized distortion
Better than Nyquist sampling     0.018 arcsecond pixels
Field of view ~ 20 arcseconds    18.4x18.4 arcsecond FOV
Dithered imaging                 Moveable focal plane mask
                                 Steering mirror in WFS
Cass focal plane ± 1mm           Focal length tolerances and alignment
AO in IR                         Possible upgrade to IR WFS, all reflective optics
              Optical Layout
Relay + Cryostat           Relay + WFS
                              Relay


                                                          Collimator OAP
ISS Exit                TFP




                                      Visible/IR Beamsplitter
           Deformable
           Mirror




                                                        Camera OAP
              Cryostat
Red Channel              Blue Channel
                                 Red Channel
Cryostat
Window
                      TFP Mask                        Array

                             Cold Stop
                             (pupil image)
                                             Filter




                             Dichroic




           Collimator OAP




                                         Camera OAP
                           Pupil Viewer

                                Image of telescope pupil,            Red channel array
                                5.04mm diameter (187 pixels)




                       Filter      Red Fold
Cold Stop                          Mirror
(Pupil image)
                                                          LiF/BaF2 Doublet Lens (in/out)
                Dichroic




                                       Red camera OAP
                      Wavefront Sensor

                                      Camera 1   Membrane
                         Collimator              Mirror


                                                  Lenslet Mirror 2
       Camera 2




TFP and Fold
from Relay

    Steering Mirror


Lenslet Mirror 1

                      Lenslet
      APDS            Array
  Optical Performance of the Science
                Channel
• Spot diagram and Strehl ratios for 17 specified
  field positions
• Through-focus spot diagram
• Encircled energy plots
• Image distortion grid plots
• Performance summary tabulation for red and
  blue channels (Strehl, spot RMS and distortion)
• Throughput
Red channel spot diagram
     0.981           0.997             0.981




             0.998   0.992   0.998




     0.997   0.997   0.992   0.997   0.997




             0.995   0.992   0.995




     0.991           0.994            0.991
Red channel through-focus spot diagram




                     pixel box                              Airy disk




 •   Through focus shown for λ = 1.25μm
 •   27μm pixels
 •   Airy disk radius = 60μm
 •   Depth of focus ~ 1mm, position found by optimization
          Encircled Energy Plots
         Red Channel      Blue Channel




• λ = 1.25 μm
• Airy disk radius 60μm
                 Image Distortion
         Red Channel                              Blue Channel




•   No specification for distortion in Gemini NICI specification
•   Distortion up to 1.7% across field, due to OAPs
•   Magnitude and orientation are the same in both channels, so real-time
    image differencing will not be affected
•   For good flat-fielding and astrometry distortion should be corrected
•   Distortion will be measured by imaging targets and corrected in data
    reduction
Science Channel Optical Performance Summary
                Red Channel                                 Blue Channel
 FIELD          STREHL   RMS    DISTORTION   FIELD          STREHL   RMS    DISTORTION
 POSITION       RATIO    SPOT   (PERCENT)    POSITION       RATIO    SPOT   (PERCENT)
 (ARCSEC)                DIAM                (ARCSEC)                DIAM
                         (m)                                        (m)
 0.00, 0.00     0.992    17.3   0.00         0.00, 0.00     0.992    17.3   0.00
 0.00, 6.45     0.997    12.2   0.88         0.00, 6.45     0.997    12.2   0.88
 0.00, -6.45    0.997    12.2   0.88         0.00, -6.45    0.997    12.2   0.88
 6.45, 0.00     0.992    17.1   0.89         6.45, 0.00     0.989    20.2   0.89
 -6.45, 0.00    0.999     8.2   0.90         -6.45, 0.00    0.999     6.8   0.90
 6.45, 6.45     0.995    13.1   1.26         6.45, 6.45     0.993    15.4   1.26
 6.45, -6.45    0.995    13.1   1.26         6.45, -6.45    0.993    15.2   1.26
 -6.45, 6.45    0.998    9.5    1.26         -6.45, 6.45    0.996    10.9   1.26
 -6.45, -6.45   0.998    9.5    1.26         -6.45, -6.45   0.996    10.9   1.26
 0.00, 9.32     0.997    10.0   1.26         0.00, 9.32     0.997    10.0   1.26
 0.00, -9.32    0.997    10.1   1.26         0.00, -9.32    0.997    10.0   1.26
 9.32, 0.00     0.994    14.7   1.28         9.32, 0.00     0.994    18.4   1.28
 -9.32, 0.00    0.997    10.5   1.29         -9.32, 0.00    0.997    13.4   1.28
 9.32, 9.32     0.991    14.9   1.79         9.32, 9.32     0.991    14.5   1.79
 9.32, -9.32    0.991    14.9   1.79         9.32, -9.32    0.991    14.5   1.79
 -9.32, 9.32    0.981    23.5   1.80         -9.32, 9.32    0.981    27.5   1.81
 -9.32, -9.32   0.981    23.5   1.80         -9.32, -9.32   0.981    27.5   1.81
Throughput of the science channel
ELEMENT                      EFFICIENCY   EXPLANATION

Relay collimator mirror      0.99         Silver overcoated with Thorium Fluoride on Silica
Deformable mirror            0.98         Silver overcoated with Thorium Fluoride on bimorph
Relay camera mirror          0.99         Silver overcoated with Thorium Fluoride on Silica

Beamsplitter dichroic        0.95         Silica substrate, dichroic reflection @ 45 deg. AOI
TFP mask                     0.982        1-5m BBAR on CaF2 substrate
Cryostat window              0.982        1-5m BBAR on CaF2 substrate
OAP collimator mirror        0.99         Gold coat on diamond turned Al.
Fold mirror                  0.98         Gold coat on Silica @ 45 deg. AOI
Spider mask                  0.90         EDM cutout
Pupil mask in/out            0.76/1.00    metal mask on 1-5m BBAR on CaF2 substrate
Cold dichroic transmission   0.94         CaF2 substrate, SpeX measured @ H
Filter                       0.80         typical transmission integrated over bandpass
Fold mirror                  0.98         Gold on Silica @ 45 deg. AOI
OAP camera mirror            0.99         Gold coat on diamond turned Al.
Detector                     0.80         Aladdin array @ 1.7m, >0.7 1-5m, Raytheon est.




Total throughput             0.33/0.43    @ 1.7m Coronographic/non-coronographic mode
  Optical Performance of the WFS
• Image quality at Membrane Mirror (Strehl,
  spot RMS diameter) as a function of field
• Image quality at optical fiber feed to APDs
  - chromatic performance of single lenslet
  - estimate of performance across field at
  lenslet/fiber interface
• Throughput
 Image Quality at the Membrane Mirror
                                      STEERING          FIELD          STREHL   SPOT
                                      MIRROR TILT       POSITION       RATIO    RMS
                                      X,Y (DEG)          ON SKY                 DIAM
• Steering Mirror is tilted to pick                     (ARCSEC )               (m)

  up stars in field and center on     0.000, -14.000    0.00, 0.00     0.99     20.0
                                      0.000, -13.857    0.00, 2.00     1.00     17.1
  MM
                                      0.000, -14.125    0.00, -2.00    0.982    28.1
• Very high Strehl (~0.99 at          0.123, -14.000    -2.00, 0.00    0.992    20.9
  0.8μm) in typical 2x2 arcsec
  dither pattern centered on          -0.123, -14.00    2.00, 0.00     0.992    20.9

  coronagraphic masks                 -0.575, -14.583   -9.32, -9.32   0.85     59.1

• High Strehl over majority of        -0.575, -13.415   -9.32, 9.32    0.73     77.0
                                      0.571, -13.415    9.32, 9.32     0.73     76.9
  9.3x9.3 arcsec field, average
                                      0.572, -14.582    9.32, -9.32    0.84     59.4
  ~0.95 decreasing to ~0.80 in
                                      -0.574, -13.999   -9.32, 0.00    0.93     35.6
  corners                             0.572, -13.999    9.32, 0.00     0.93     35.5
                                      -0.001, -14.483   0.00, -9.32    0.87     30.1
                                      -0.001, -13.416   0.00, 9.32     0.84     60.1
       Image quality of lenslet/fiber pair

Lenslet/fiber       SF6 plate      100μm diameter fiber
interface




                Plano-convex BK7
                lens EFL 24mm



• 0.5-0.9μm spots small compared to 100μm diameter of
  optical fiber
• → model with paraxial lens to check performance across
  field
Image quality at lenslet/fiber optic interface

                            TILT X,Y          FIELD          SPOT
                            (DEG)             POSITION       RMS
                                               ON SKY        DIAM
                                              (ARCSEC )      (m)

• Lenslet modeled by        0.000, -14.000    0.00, 0.00     2.30

  paraxial lens             0.000, -13.857    0.00, 2.00     3.37

                            0.000, -14.125    0.00, -2.00    1.36
• Spots small compared to   0.123, -14.000    -2.00, 0.00    2.40
  100μm diameter of         -0.123, -14.00    2.00,   0.00   2.40

  optical fiber             -0.575, -14.583   -9.32, -9.32   2.80


• Optical performance at
                            -0.575, -13.415   -9.32, 9.32    9.34

                            0.571, -13.415    9.32, 9.32     9.35
  feed to APDs is very      0.572, -14.582    9.32, -9.32    2.79
  good                      -0.574, -13.999   -9.32, 0.00    4.02

                            0.572, -13.999    9.32, 0.00     4.02

                            -0.001, -14.483   0.00, -9.32    2.03

                            -0.001, -13.416   0.00, 9.32     8.11
                   Throughput of the WFS
ELEMENT                   EFF    EXPLANATION
Relay collimator mirror   0.98   Silver overcoated with Thorium Fluoride on Silica
Deformable mirror         0.98   Silver overcoated with Thorium Fluoride on bimorph
Relay camera mirror       0.98   Silver overcoated with Thorium Fluoride on Silica
Beamsplitter dichroic     0.95   Silica substrate, dichroic transmission
WFS fold 1                0.97   Silver overcoated with Thorium Fluoride on Silica @ 45 deg. AOI
WFS fold 2                0.97   Silver overcoated with Thorium Fluoride on Silica @ 45 deg. AOI
WFS collimator mirror     0.98   Silver overcoated with Thorium Fluoride on Silica
Steering mirror           0.98   Silver overcoated with Thorium Fluoride on Silica
WFS camera 1 mirror       0.98   Silver overcoated with Thorium Fluoride on Silica
WFS camera 2 mirror       0.98   Silver overcoated with Thorium Fluoride on Silica
Membrane mirror           0.92   Aluminum coating on nitro-cellulose substrate
Lenslet mirror 1          0.98   Silver overcoated with Thorium Fluoride on Silica
Lenslet mirror 2          0.98   Silver overcoated with Thorium Fluoride on Silica
Lenslet array             0.9    lenslet dead space
Optical fiber             0.9    coupling efficiency, fiber losses
APD                       1.00   Photon counting




Total throughput          0.55   @ ~0.75m
              Optical Tolerancing
• Tolerancing of fabrication and assembly parameters is done with
  Zemax EE Version 10
• Figure errors are dealt with separately
• Merit criteria used is wavefront RMS
• Sensitivity analysis computes change in system wavefront RMS for
  each tolerance individually. Aggregate performance estimated by
  RSS and is used to identify tolerances which need to be tightened
  (worst offenders)
• Monte Carlo analysis simulates effect of all tolerances
  simultaneously giving more accurate simulation of real-world
  performance
• Separate analysis is used to assess the sensitivity of optical bore-
  sight to tilts and decentrations (for mechanical design and
  alignment)
      Tolerancing of Relay + Cryostat Red Channel
                Tolerance values                            Monte Carlo Simulation (50 trials)

PARAMETER                 VALUE    UNITS            λ=1.25μm     MERIT FUNCTION      STREHL RATIO
Thickness (TTHI)          0.10    mm                           (wavefront RMS/μm)

Decentration (TSDX/Y)     0.10    mm               Nominal      0.0101              0.997

Runout (TIRX/Y)           0.05    mm               Best         0.0095              0.997

Radius (TFRN)             0.20    fringes@0.63m   Worst        0.0126              0.985

Conic constant (TCON)     0.005   dimensionless    Mean         0.0105              0.990

Conic decentration        0.3     mm               Std Dev      0.0006
(TEDX/Y)




•    Focus compensation allowed at cassegrain focus (±0.4mm)
•    All tolerances are typical of standard fabrication and assembly except conic
     decentration which is relaxed from ±0.05mm to ±0.3mm at vendor’s request
•    Analysis predicts Strehls better than 0.98 at λ=1.25μm (surface figure not included)
                     Tolerancing of Relay +WFS
                Tolerance Values                       Monte Carlo Simulation (50 trials)

PARAMETER                VALUE     UNITS                      MERIT FUNCTION       STREHL RATIO
                                                    λ=0.8μm
Thickness (TTHI)         0.10     mm                         (wavefront RMS/μm)

Decentration (TSDX/Y)    0.10     mm               Nominal   0.025                0.976

Runout (TIRX/Y)          0.05     mm               Best      0.016                0.980

Radius (TFRN)            0.20     fringes@0.63m   Worst     0.042                0.93

Conic constant (TCON)    0.005    dimensionless    Mean      0.027                0.97

Conic decentration       0.3      mm               Std Dev   0.006
(TEDX/Y)




•    Focus compensation allowed at cassegrain focus (±1.00mm)
•    All tolerances are typical of standard fabrication and assembly except conic
     decentration which is relaxed from ±0.05mm to ±0.30mm at vendor’s request
•    Analysis predicts Strehls better than 0.93 at λ=0.8μm (surface figure not included)
                       Optical Flexure
                                                       Flexure of cryostat only
                                              TELESCOPE       SCIENCE   X/MM     Y/MM
                                              ORIENTATION     CHANNEL
• Mechanical FEA model gives                  Zenith          Red       0.000    0.000

  decentrations and tilts of optical          Zenith          Blue      0.000    0.000

  components as a function of
                                              +70 x           Red       -0.031   -0.054
  telescope orientation (zenith, +70          +70 x           Blue      -0.059   -0.113
  deg in x and +70 deg in y)
• These perturbations are entered             +70 y           Red       -0.032   -0.001
                                              +70 y           Blue      0.033    -0.004
  into the raytrace and the relative
  on-axis movement of the red and                  Flexure of cryostat + WFS
  blue science channels measured              TELESCOPE       SCIENCE   X/MM     Y/MM
                                              ORIENTATION     CHANNEL
•   Typical movement about 4 pixels from      Zenith          Red       0.000    0.000
    zenith to 70 degrees and about 2 pixels   zenith          Blue      0.000    0.000
    relative movement between the red and
    blue channels from zenith to 70           +70 x           Red       0.021    -0.035

    degrees                                   +70 x           Blue      -0.008   -0.097


                                              +70 y           Red       -0.038   0.014
                                              +70 y           Blue      0.027    0.011
Optical Flexure
 Movement scaled to
 pixels per hour (linear
 scale from 70 deg to
 15 deg)

								
To top