1. ISUAL Sprite Imager The Effects of Mask Pinholes: Test Results
Stewart Harris

2. CCD Active Area Masking
F/O Assembly Procedure
F/O Window cemented to CCD
Exposes full CCD Active Area
Mask deposited on f/o taper
F/O taper cemented to window
Remaining area of window is painted with Z306
Image intensifier is cemented to top of taper (not shown)
Top view of Dalsa CCD with f/o assembly
Fiber Optic Taper
Fiber Optic Window
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

3. Testing Effects of Mask Pinholes
Mask is applied to small end of taper
Initial masks done at Sine Patterns
poor quality, scratches, many pinholes
Masks done at SSL (Jim Malloy)
Inconel deposited in layer ~3000Å thick
Edge defined by razor blade
All tapers have exhibited some pinholes
More recent trials have shown very few (~ 6 pinholes visible)
This test was contrived to determine the effects of these pinholes
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

4. Effects of pinholes - Imaging Modes
Aurora
Each exposure is taken then immediately shifted into readout area
This mode has miniscule contamination from pinholes
Sprite Continuous
Exposures are “stacked up” in masked area
Therefore, each exposure can be contaminated by light coming through pinholes during subsequent exposures
Sprite Burst
Same problem as Continuous Mode
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

5. Continuous Mode Image Stacking
The active image area not covered by the mask is normally painted black, but this step can only happen after the taper is cemented to the window, and was inappropriate for this test.
In Continuous Mode, successive images are clocked into the “pseudo-masked” area. Since the circular mask on the taper only covers a portion of the CCD active image area, there are artifacts of the taper edge in the test images.
In Aurora Mode, each image is immediately shifted into the readout area, therefore aurora images are more immune to the effects of pinholes. For this reason they make good baseline images with which to compare the Continuous Mode images.
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

6. Pinhole Test Description
One cemented assembly used
CCD-200 assembled with Incom-1 taper
Three un-cemented assemblies tested
Used CCD-213 with f/o window cemented
Tapers with mask deposited butted to it
Incom-5, Schott-1, Schott-2
Take images with uniform illumination
In both Continuous and Aurora Mode
Take images with active area blocked
Block active area, but leave masked area illuminated
This exaggerates effects of pinholes
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

7. Images - Continuous Mode
Incom-1 (cemented on CCD-200, and painted)
Incom-5 (not cemented, not painted)
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

8. Images - Continuous Mode
Schott-1 (not cemented, not painted)
Schott-2 (not cemented, not painted)
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

9. Analysis of Difference Images
Move a small Black cover over our reduced image area, leaving masked area fully illuminated
Increase illumination to “Xtra” level to exaggerate pinhole illumination
Take both an Aurora Image and Continuous Mode Image
Difference Image = Continuous - Aurora
Enhance Difference Image to expose pinholes (sharpen edges)
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

10. Difference Images - Black Xtra
Schott-1 (not cemented)
Incom-1 (cemented and painted on CCD-200)
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

11. Difference Images - Black Xtra
Schott-2 (not cemented)
Incom-5 (not cemented)
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002

12. Conclusions Schott-1 Schott-2 Incom-5
Has a few (7) very dim pinholes, amount of contamination minimal
Useable “as-is” for flight unit
Schott-2
Has significant edge problem (left edge of mask)
Looks like it’s on outside edge of mask
Also has a few (1-2) very dim pinholes
Satisfactory for ETU, normal painting should minimize light leak on edge
Perhaps some black paint on edge before cementing, need to experiment
Incom-5
Has one significant pinhole (center right) and a few (6) dim ones
Quite satisfactory for ETU
Incom-1 (already cemented to CCD-200)
Has major pinhole (lower right) and many small ones (1st SSL mask)
Is OK for ETU, especially useable for mechanical testing
NCKU UCB Tohoku Sprite Imager S. Harris
21 Feb 2002