Use of a Digital Micromirror
Array as a Configurable Mask in
Optical Astronomy
Shawn Gilliam
Advisor: Dr. William Hetherington
Research Associate: Teal Pershing
DMA Apparatus
Telescope
DMA
Lens
CCD
• 12” Cassegrain Telescope
• Digital Micromirror Array
• Charge Coupled Device
2
Optical Transfer Function
Zoomed
ℱ{𝐼𝑖 (𝑋, 𝑌)}
= ℱ{𝑝𝑠𝑓 𝑥, 𝑦 }
ℱ{𝐼𝑜 𝑥, 𝑦
3
Coronagraph
4
Lyot Stop
Aperture Masking
Interferometry
Primary
Secondary
Tertiary
Aperture Mask
Bold black
represents the
section of the
primary mirror that
is passed through
the system.
5
• Backlit holes in black cardboard with 0.5 cm
separation, at 10 m.
• Angular separation of 100 ±20 arcseconds.
Dim Center Star
6
• Pixels of a monitor, configured to a separation
of 0.216 mm at 13 m.
• Angular separation of 3.4 ±0.1 arcseconds.
7
• LED’s, one much brighter than the other,
placed 0.4 cm apart at 40 m.
• Angular separation of 25 ±5 arcseconds.
8
Profile plot across image at x = 370
300
Saturation
250
Unmasked
Photon Count
200
Masked
150
100
Peak
50
0
0
100
200
300
400
500
600
Position (pixels)
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Other Achievements
• Fourier Transform Lab used in PH 481.
• Fresnel Zone Plate Mask Designs.
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Conclusion
• The DMA Apparatus is a useful tool for optical
astronomy.
• Angular resolution of 3.4 ±0.1 arcseconds.
• Light from bright sources can be reduced.
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Future Directions
• Construct a workable apparatus that can be
used for night viewing.
• Obtain a complete description of the Optical
Transfer Function.
• Incorporate a variety of masking techniques.
12
References
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•
•
•
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[1] “Robust Coronagraphy with an APP.” [Online]. Available:
http://home.strw.leidenuniv.nl/~kenworthy/research/app/. [Accessed: 04-Jun-2012].
[2] Wikipedia contributors, “Coronagraph,” Wikipedia, the free encyclopedia. Wikimedia
Foundation, Inc., 16-May-2012.
[3] “DLP System Optics” Application Report DLPA022, Texas Instruments, July 2010.
[4] Wikipedia contributors, “Speckle imaging,” Wikipedia, the free encyclopedia.
Wikimedia Foundation, Inc., 17-Mar-2012.
[5] “Presentation of the DLP Technology: Presentation part-one.” [Online]. Available:
http://us.generation-nt.com/technology-dlp-video-projector-digital-light-processingreview-42606-2.html [Accessed: 05-Jun-2012].
[6] “Mimir Photo Archives – 20021217.” [Online]. Available:
http://people.bu.edu/clemens/mimir/Photo_Archive_Pages/20021217.html
[Accessed: 05-Jun-2012].
[1]“APOD: 2008 January 11 - Polaris Dust Nebula.” [Online]. Available:
http://apod.nasa.gov/apod/ap080111.html. [Accessed: 11-Jun-2012].
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14
Fourier Transforms
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Fresnel Zone Plate
16
f
f/3
•
f < f/3
f/7
17