NICI Optical Design and Performance SDN 1007

1. NICI Optical Design and Performance SDN 1007 • Science derived optical requirements • Layout • Performance • Tolerancing • Optical flexure

2. Science Derived Optical Requirements

3. Optical Layout Relay + WFS Relay + Cryostat

4. Relay Collimator OAP ISS Exit TFP Visible/IR Beamsplitter Deformable Mirror Camera OAP

5. Cryostat Red Channel Blue Channel

6. Red Channel Cryostat Window TFP Mask Array Cold Stop (pupil image) Filter Dichroic Collimator OAP Camera OAP

7. Pupil Viewer Image of telescope pupil, 5.04mm diameter (187 pixels) Red channel array Filter Red Fold Mirror Cold Stop (Pupil image) LiF/BaF2 Doublet Lens (in/out) Dichroic Red camera OAP

8. Wavefront Sensor Camera 1 Membrane Mirror Collimator Lenslet Mirror 2 Camera 2 TFP and Fold from Relay Steering Mirror Lenslet Mirror 1 Lenslet Array APDS

9. 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

10. Red channel spot diagram 0.981 0.997 0.981 0.998 0.992 0.998 0.997 0.997 0.997 0.992 0.997 0.992 0.995 0.995 0.991 0.991 0.994

11. 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

12. Encircled Energy Plots Red Channel Blue Channel • λ = 1.25 μm • Airy disk radius 60μm

13. 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

14. Science Channel Optical Performance Summary Red Channel Blue Channel

15. Throughput of the science channel

16. 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

17. Image Quality at the Membrane Mirror • Steering Mirror is tilted to pick up stars in field and center on MM • Very high Strehl (~0.99 at 0.8μm) in typical 2x2 arcsec dither pattern centered on coronagraphic masks • High Strehl over majority of 9.3x9.3 arcsec field, average ~0.95 decreasing to ~0.80 in corners

18. Image quality of lenslet/fiber pair 100μm diameter fiber Lenslet/fiber interface SF6 plate 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

19. Image quality at lenslet/fiber optic interface • Lenslet modeled by paraxial lens • Spots small compared to 100μm diameter of optical fiber • Optical performance at feed to APDs is very good

20. Throughput of the WFS

21. 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)

22. Tolerancing of Relay + Cryostat Red Channel Tolerance values Monte Carlo Simulation (50 trials) (wavefront RMS/μm) • 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)

23. Tolerancing of Relay +WFS Tolerance Values Monte Carlo Simulation (50 trials) λ=0.8μm (wavefront RMS/μm) • 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)

24. Optical Flexure Flexure of cryostat only • Mechanical FEA model gives decentrations and tilts of optical components as a function of telescope orientation (zenith, +70 deg in x and +70 deg in y) • These perturbations are entered into the raytrace and the relative on-axis movement of the red and blue science channels measured • Typical movement about 4 pixels from zenith to 70 degrees and about 2 pixels relative movement between the red and blue channels from zenith to 70 degrees Flexure of cryostat + WFS

25. Optical Flexure Movement scaled to pixels per hour (linear scale from 70 deg to 15 deg)