1. Intra-pixel Sensitivity Testing Preliminary Design Review
3 August Stella Jang
SPACE
TELESCOPE
SCIENCE
INSTITUTE

2. Goals Present the calibrated target/ 3-axis stage design
Present requirements for blackbody radiation contrast and pixel saturation
Show that the proposed design meets the necessary requirements
Show that required tolerances can be met
Approve a plan for moving from PDR to CDR
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3. Definition of Intra-pixel Sensitivity
Ni,j =number of electrons/second detected in pixel i,j
ei,j(x,y) =intra-pixel sensitivity at x,y in pixel i,j
I =number of photons/second arriving at x,y in pixel i,j
j+2
j+1 j i
i+1
i+2
i+3
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4. Definition of Intra-pixel Sensitivity
Figure 8. DRM-quality photometry (1%) cannot be achieved according to our measurements of intra-pixel sensitivity. (Left) Intra-pixel sensitivity of HgCdTe to a point source measured by Co-I Finger. (Right) NICMOS magnitude errors as a function of intra-pixel source location (Stiavelli, private communication).
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5. IPS Experiment Requirements (from TFST0900, Table 1)
Wavelength range
0.5 – 5.5 mm
Sampling
5x5 – 10x10 per pixel with 1%relative position error
Image size
< 5 mm FWHM over 10 x 10 pixel central region, no requirement outside this area
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6. NGST Requirements NDC0200 (from NGST Doc. #641)
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7. Modules pinhole Offner light source light guide focal reducer
3-axis stage
filters
window
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8. Layout with f/1.5 focal reducer
45° flat
45° flat
Offner
secondary
f/10 point
source
detector
focal
reducer
filter
window
Offner
primary
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9. Shaded model -- with focal reducer
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10. Close-up of f/1.5 focal reducer
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11. Modules Requirements
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14. PSF
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15. 10 x 10 pixel field (l = 5 mm)
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16. Flux Equation T =temperature of source
QE =absolute quantum efficiency of detector
Toptics =transmission of window, mirrors, and central obscuration of the focal reducer
Tvar =variable transmission at light guide exit port
TPK50 =transmission of PK50 blocking filter
Tfilter =transmission of bandpass filter
W =solid angle subtended by entrance pupil at source
A =area of emitting surface
ti =integration time
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17. T=300K
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18. T=3250K
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20. PK light guide
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21. Johnson-R
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22. Johnson-R
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23. Johnson-I
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24. Johnson-I
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25. J
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26. J
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27. H
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28. H
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29. K
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30. K
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31. L’
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32. L’
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33. M’
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34. M’
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35. Software Requirements
Integrated control software
exposure (multi-plane FITS)
filter wheels
3D stage
light source (on/off and intensity)?
Analysis software
data reduction pipeline
IDL
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36. Designs Light source - Coherent quartz tungsten halogen -150W/3250K
- Variable intensity
Light guide - Coherent 24” multi-fiber gooseneck
- 5.54mm exit port diameter
Pinhole - 5 mm diameter in a 1” retaining ring mount
3-axis stage - 3 Newport compact motorized translation stages
- Newport motion controller
Window mm
- 10mm thickness
- Mounted in end plate of dewar.
Filters - Johnson-R, Johnson-I, J, H, K, L’, M’, PK50
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37. Designs (cont’d) Offner relay - Re-images source 1:1 onto detector
Allows decent imaging at f/10 over full 2K2 field
Provides excellent imaging over a smaller central region
Compact, folded design fits available space
All reflective optical design is free from chromatic aberration
Focal reducer - Produces f/1.5 beam for sub-pixel imaging
At f/10, diffraction-limited FWHM = 22.6 mm (l = 2.2 mm)
At f/1.5, diffraction-limited FWHM is = 3.4 mm (l = 2.2 mm)
Single-element optic with 4 different surface radii (2 elliptical, 2 spherical)
Reflective coatings on the two elliptical surfaces
Parfocal with f/10 beam, designed to reside in a filter wheel
Provides subpixel imaging over a 10 pixel diameter region
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38. Designs
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39. Hardware Set-up
3-axis motion stages are assembled and attached to the motion driver
Pinhole and light source needs to be attached to axis stage
Flux from light guide exit port must be variable
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40. Notes on Schedule Some hardware not ordered yet
Anticipate that the hardware will be complete no earlier than December
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41. Open Issues Controlling efficiency at the light guide exit port
This has implications for the pinhole/stage design
M’ filter bandwidth
How to suppress flux for wavelength < 4 mm ?
Monochromator vs. Filters
Cost
Time
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