1. Vortex Coronagraphy G. Serabyn Jet Propulsion Laboratory,
California Institute of Technology
A. Carlotti (IPAG), J. Hoffman (JH), D. Mawet (ESO),
C. Norman (HST), L. Pueyo (HST), N. Kasdin (Princeton)
ACWG2.5
Oct 24, 2013
Copyright 2013 California Institute of Technology. Government sponsorship acknowledged.
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2. The Vortex Coronagraph
A vortex phase shifter applies a helical phase to focal plane Airy field
Coronagraphic
Image
Input
pupil
Focal
plane
Pupil
plane
bypass
vortex
 = eim
through
vortex
LCP mask
PC mask
Lyot stop
Advantages: Phase mask  -Small IWA (chg. 2: 0.9 λ/D; chg. 4: 1.7 λ/D)
(no central block) -High throughput
-Clear 360 azimuthal FOV
-Layout: simple: common w. Lyot, shaped pupil

3. Liquid Crystal Polymer (LCP) Vector Vortex Masks
JDSU:
Orientation
defined by slit
Beamco:
Orientation defined by line focus
Central defect ~ 1 micron
Charge 4
vortex:
axis spins
2x as fast
JDSU Second Gen.
Covered central defect ~ 30 – 40 m

4. 10% bandwidth test on JDSU gen 2 mask; 3-8 λ/D
10% BW
avg. contrast
for 3-8 λ/D =
1.1 x 10-8
(dominated by
one bright
dust speckle)
5.0 x 10-9
without bright speckle
Used five 2% filters
Wavefront control using all 10% BW

5. Vortex Mask Performance for 10% BW
9 x 10-9 average contrast over 1.5 to 9.5 λ/D dark hole for 10% BW
dominated by a few dust particles or defects; new mask in hand
Soon to test a 25% bandwidth mask

6. Broadband Performance
Three approaches to broadband:
Spectral Polarization Filtering:
Multi-layer half-wave-plate vortex:
LCP layers rotate (twist) as a function of depth
Working with three companies:
JDSU:
New mask with 30 mu defect and cover is here
Future: potentially, a classical broadband three-layer mask
Beamco:
Reduce central defect to insignificance; no central cover
25% BW twisted multi-layer mask with 3 micron defect is here
Below 10-8 monochromatically with no cover
North Carolina State:
Lay down opaque spot first as reference; twisted multi-layer 20% BW; mid-range defect size; contract in place

7. Obscured Pupil Sources of Contrast Degradation
On-axis secondary
Secondary support legs
Other small nubs
Does the vortex coronagraph have solutions for all of these?
Yes, in general; Vortices on Palomar, Subaru, VLT, LBTI
So, what’s the problem?
Promising solutions for the highly obscured input pupil recently proposed; basic codes now exist (written by Europeans)
And B
from Palomar:
contrast ~ few 10-5
HD141569:
Wahl et al.,
in prep.

8. Aperture Blockage: Two part solution:
Several solutions for a secondary obstruction:
Dual-stage vortex: (d/D)^4 rejection for charge 2
Three stage vortex: perfect rejection, but lots of optics
Apodized vortex (Mawet et al. 2013):
perfect rejection with few optics
Solution for the spider support legs:
ACAD: Active Correction of Aperture Discontinuities
(Pueyo and Norman 2013)

9. The Ring Apodized Vortex
require 0 in outer ring
Input Pupil
2nd Lyot Pupil
Mawet et al. 2013

10. RAVC charge 4: Add a ring
Theoretical throughput for transmissive apodizer
Transmission low for high charge
and large obscurations

11. Current AFTA Vortex Layout Provides a Pupil Usable for an Apodizer similar to band-limited & shaped pupil (at least)
apodizer
vortex

12. ACAD for Vortex Coronagraphs
ACAD + RRAVC
(Pueyo, Mawet, et al.):
2.0λ/d, 33% BW
~70% throughput (l=2), ~50% (l=4)
(or a PIAA-like solution for spider)
Pueyo et al. 2012, 2013

13. Solution Options Options Throughput SP-AVC + ACAD high RAVC + ACAD med
low
Key:
SP-AVC: uses shaped pupil apodizer
RAVC: uses uniform apodizer
Two types of apodizer: “uniform ring” or “shaped pupil”

14. Submitted Vortex Solution: ACAD
Hoffman, Norman, Pueyo
Stroke ~ 1 micron along supports; max ~ 1.5 microns in small region

15. Optimized “shaped pupil’’ apodizer for AFTA
“Camouflaging the support legs
Increased throughput by relaxing strict zero-flux condition
Light can be present at high spatial frequencies
Mask throughput 47%
apodizer
Lyot stop
A. Carlotti et al. 2013, SPIE ,

16. Predicted Contrast for Submission
IWA ~ 3λ/D
Can see closer in

17. Transmission and Search Space
Maximum system transmission ~ 11%
IWA ~ 3.0 λ/D
OWA ~ 19 λ/D
IWA
OWA

18. Yield of RVs

19. Conclusions and Disclaimer
New software hurriedly written and debugged to evaluate the vortex option for the recently-cleared AFTA pupil
Lots being learned in a hurry
Final parameter errors found and fixed
A vortex solution with a system transmission of 11%, and IWA ~ 3 λ/D has been identified