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The Optical Vortex Coronagraph
Erin L. Ford
Advisor: Prof. Grover Swartzlander
College of Optical Sciences
Optical Vortex Laboratory
– Rukiah Abdul-Malik
– Joshua Kim
Veeco, Inc.
Steward Observatory
– Prof. Laird Close
– Mary Anne Peters
Jet Propulsion Laboratory
– Joanna Schmit
Support: US Army Research Office
– David Palacios
– Dan Wilson
Strategy
• Demonstrate OVC principles using a
charge 2, non-achromatized vortex lens
• Uncover potential design problems
when coupled to telescope
• Determine vortex lens fabrication
issues and resulting theoretical
performance
Optical Vortex Lens
• Glass Optical Element
• Pitch =1 Wave Phase Delay
Δd
• Transmission:
t = exp(i2θ) at λ0
• Topological Charge:
m(λ) = m0 λ0/ λ ≈ 2
Charge m=2 vortex lens
Creating a Black Hole
Image of Star
Pupil Plane
Fourier Transform
FT{f(r)}
f(r)
m=0
m=2
Mawet, Riaud, Absil, Surdej (AJ. 2005)
Foo, Palacios, Swartzlander (Opt. Lett. 2005)
FT{f(r)exp(i2θ)}
Coronagraph Design Principles
The Optical Vortex Coronagraph is a Lyot-type coronagraph with a
phase mask instead of an occulting disk
L1
Aperture
Stop
L2
Lyot Stop
Vortex
mask
L3
Imaging system
L4
Camera
planet
star
f1
f2
f3
f3
z
Coronagraph Design Principles
The Optical Vortex Coronagraph is a Lyot-type coronagraph with a
phase mask instead of an occulting disk
L1
Aperture
Stop
L2
Lyot Stop
Vortex
mask
L3
Imaging system
L4
Camera
planet
star
f1
f2
f3
f3
z
Telescope system
Adaptive
Optics
Camera
Fold
Mirror
Refractive
Telescope
Image of the
telescope pupil
f = 50mm
99% Strehl
f = 100mm
Fold mirror
Fold
Mirror
f = 25mm
Vortex
f = 100mm
f = 100mm
Optical Vortex Coronagraph
Adaptive Optics Talk
Mary Anne Peters
Wednesday 11:30 AM
Camera
Experimental Results
Off-Axis Source
On-Axis Source
Exit Pupil Images: Integrated Intensity Ratio: 63
Laser Measurements at 785nm
E-Beam Vortex Lens Analysis
Measured
Profilometer
Ambiguity
Ebeam
Stitching
Errors
(False Color Surface Profiles)
“Corrected”
Numerical Model
4096 x 4096
Numerical Arrays
800x800 cropped images
Focus at Vortex Lens
Transmitted Phase
( m=2 )
4096
Numerical Predictions
Entrance Pupil
Image (m=2)
Exit Pupil
Image (m=0)
Integrated
Intensity
Ratio:
72 (vs 63)
Summary
1. Optical Vortex Coronagraph - described
2. Designed system for demonstration on sky
First light in 1 month
3. Requires a tip/tilt adaptive optic system – 99% Strehl
4. Vortex lens from JPL using e-beam lithography
Fabrication issues identified
5. Expected contrast of 104 at 4_/D
250 times improvement!
Lee, Foo, Johnson, Swartzlander (PRL 2006)
Untold improvement over original proposal
Swartzlander, (Opt. Lett. 2001)