a single-mode nulling rotating coronagraph for high...
Post on 19-Feb-2021
0 Views
Preview:
TRANSCRIPT
-
1
A Single-Mode Nulling RotatingCoronagraph for High Contrast
Ground Based Imaging
Bertrand MennessonGene Serabyn, Stefan Martin and Kurt Liewer
Caltech / Jet Propulsion Laboratory
Spirit of Lyot ConferenceBerkeley, June 4-8, 2007
“Batiment” Lyot at the Paris Observatory(Meudon site)
Where COME-ON, FLUOR, NAOS etc were conceived, tested and partly assembled
-
2
Current limits for high contrast / high resolutionground based imaging: single telescopes
Classical Lyot coronagraphs: central 4-5 λ/D is not accessible
Apodized coronagraphs and phase mask coronagraphs: cantheoretically image companions at λ/DHigh dynamic range inside 3-4 λ/D only accessible with very highStrehl (> 90% restricted to small D or future ExAO systems)
Speckle interferometry: imaging at λ/D, dynamic range of a few tens
Aperture masking (Keck, Palomar): allows imaging within λ/D butwith dynamic range still limited by V accuracy (fibers would help)
Current off axis point source detection limit:~1000:1 at 5λ/D, degrading to ~100:1 at λ/D
Current limits of high contrast /high resolutionground based imaging: long baseline
interferometers
Very high angular resolution (down to ~1mas in thenear IR), but dynamic range limited to:
20-30:1 for conventional (bulk optics) interferometers
~100:1 using single-mode waveguide recombination andphotometric calibration (FLUOR)
~100:1 or better using nulling in the mid–IR (MMT, KECK,LBTI). Nulling brings extra spatial resolution
Contrast limit for detection of off-axis sourcesis ~100:1
-
3
Bridging the gap: near IR fiber nulling ona single-telescope
Principle: rotating nuller feeding a single-mode fiber
0
0.25
0.5
0.75
1
0 1 2 3 4 5 6
Rotation Angle (radians)
Tra
ns
mis
sio
n
I:
IIa:
Fix
edd
ual-
ap
ma
sk
Pu
pil
Rota
tor
Rota
tin
g d
ual-
PM
SMF
SMF Pu
pil
Rota
tor
Nu
ller
SMF
Fix
ed s
ingle
-ap
maskIII:
Ph
ase
Sh
ifte
r (R
/F)
Fix
ed A
PS
Lig
ht
from
tele
scop
eL
igh
t fr
om
tele
scop
e
Lig
ht
from
tele
scop
e
Fix
edd
ual -
ap
mask
Pu
pil
Rota
tor
IIb:
Nu
ller
Lig
ht
from
tele
scop
e
SMF
I:
IIa:
Fix
edd
ual-
ap
ma
sk
Pu
pil
Rota
tor
Rota
tin
g d
ual-
PM
SMF
SMF Pu
pil
Rota
tor
Nu
ller
SMF
Fix
ed s
ingle
-ap
maskIII:
Ph
ase
Sh
ifte
r (R
/F)
Fix
ed A
PS
Lig
ht
from
tele
scop
eL
igh
t fr
om
tele
scop
e
Lig
ht
from
tele
scop
e
Fix
edd
ual -
ap
mask
Pu
pil
Rota
tor
IIb:
Nu
ller
Lig
ht
from
tele
scop
e
SMF
FIBER NULLER POSSIBLE IMPLEMENTATIONS
Multi-Axial Co-Axial
-
4
Possible Nulling Beam Combinations
Co-axial recombination:+ Variety of solutions provide achromatic nulls:RSI: rooftops, periscopes, LSI: dielectric plates + MMZ+ Proven techno (Wallace, Serabyn, Mennesson etc)
Multi-axial recombination:Beam combiner = focusing element + fiber+ Easier to implement on telescope+ Adaptability to a large number of sub-beams- Deep nulls unproven before 2005- Fiber injection efficiency lower
“A la FLUOR or IONIC” Would need zero dispersion waveguides e.g. photonic fibers
A:
B:
C:
1
2
1
2
1
2A:
B:
C:
1
2
1
2
1
2
1
2
1
2
1
2
1
2
The Multi-axial (Fiber) Combiner
SM Fiber provides 2 in 1: Beam Combination and Spatial Filtering
-
5
Lab results: visible LASER
Lab results: visible LASER
A
D
C B
E
F
G
A
D
C B
E
F
G
-
6
Lab results: visible LASER
Best nulls are 1.3x10-6 (from Haguenauer & Serabyn, Applied Optics, 2006
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
50 70 90 110 130 150 170
Time (s)
Nu
ll d
ep
th
Lab results: white lightDielectric Plates
-
7
Lab results: white light
Dual Polarization Stable White Light (1.5 to 1.8 microns) Null Level: ~6x10-5
Multi-axial recombination (Mennesson et al. 2007 in prep)
Key Advantages High contrast accessible without high Strehl (fiber corrects
individual wavefronts)
Ultimate contrast fixed by OPD rms over unit integration time K band Nulls of 1e-3 readily accessible using 10ms sampling
Spatial resolution = λ/2B (56 mas in K with B=4m), half transmissionpoint is λ/4B =28 mas
Null level is constant over FOV. Achievable detection limit is fixedby fringe pattern Tr, not by field dependent residuals
Can theoretically achieve 500:1 detection at λ/D in the near IR
Much simpler to implement than long baseline interferometry;baseline can rotate much faster
-
8
Limitations• FOV limited to diffraction limit of sub-aperture λ/d ~ 3-4λ/D. Really
tailored to high angular resolution.Could work in conjunction with conventional coronagraph accessinglarger separations
• Sensitivity loss wrt to full telescope• Both limitations reduced when using more small sub-apertures
Injection efficiency into a singlemode fiber using b/d =3.5m/1.5m(Multi-axial combination, nodensification, Palomar 200 inch) at2.2 microns. Plain curve:constructive case. Dotted curve:nulling case. A denser pupil, asavailable on Keck or Subaru, willallow better on-axis couplingefficiency, up to 62% in the idealcase where b=d Dotted curve:nulling case.
Simulated Performance of Palomar system:two 1.5x3m sub-apertures 3.5m apart
K band signal detected over 60 baseline rotations (5s each, sampled at 100Hz)
Left: mK=3 star with 500 times dimmer companion 40 mas away
Right: same but with companion 180 mas away
-
9
Objectives of Fiber Nuller Set-up atPalomar 200”
Technical goals:- Prove feasibility of the approach on the sky- Demonstrate detection of companion at the 500:1 level within100 mas of primary (e.g. composite spectrum stars)- Test TPF-I companion detection approach on the sky underfavorable conditions
Science goals:- Stellar diameters, atmospheric layers, asymmetries (evolvedstars easily resolved)- Survey of hot material around mK
-
10
Palomar layout
Palomar Layout
-
11
r
Palomar 1st Engineering run (May 07)
• Mounted FN bread-board in 200” Cassegrain cage,behind PALAO system
• Injected starlight from both beams into K band SM fiber
• Checked angle tracker (quad cells), photometriccalibration wheel and K photometer sensitivity (presentlylimited to mK=5 at constructive peak)
• Under Jet Stream: strong winds, bad/fast seeing (~2”)made fiber injection unstable
-
12
Future Developments• November 07 engineering run goals:
- Measure first nulls- Enable aperture rotation
• Key upgrades (2008 = present limit of funding):- Low noise fast read IR camera- Enable fringe tracker to further decrease opd
residuals left after AO (larger sub-apertures than AO)- Install refraction corrector- Use dispersion and spectral differential nulling- Use >2 sub-apertures (deeper central nulls, or try nulling + DP)
• > 2008: Get to larger telescope at a prime astronomical site. Southhemisphere preferred to survey nearby young stars
• Possible FN in space on a 1.5m vis/near IR astrometric telescope(Pravdo et al. 2007)
Related presentations:
• Talk by M. Shao (Tuesday 11:30 am):Visible nulling coronagraphy
• Poster by G. Perrin et al. :Diffraction limited high dynamic range imaging from thevisible to the infrared
-
13
Back up slides
Advantages
• High contrast accessible without highStrehl (fiber corrects individual wavefronts)
• Ultimate contrast fixed by rms of opticalpath difference over unit integration time:
• N=1/4 (t2 + σ2φt) N=1e-3 readilyaccessible with 10ms sampling in K
-
14
Palomar layout
Palomar Layout
-
15
Multi-axial Beam Combination
• After densification, can adapt to the case fmany-sub-apertures:
-
16
Expected performance at Palomar
top related