Multi-aperture Instantaneous Interferometric Imaging of Extended &

Moving Objects by Phase Optimized Spatial Filtering

Luc Damé, Xiyang Fu, Virginie Maury & Christophe MontaronService d'Aéronomie du CNRS & LESIA Meudon Observatory, France

ICSO 2006Conference on Space OpticsESTEC, Noordwijk, 29/06/2006

Lyman 40"x40" – VAULT/NRLSOLARNET/SPI - PROTEUS

Context – a Short History

• Solar interferometry, DIRECT IMAGING OF AN EXTENDED FIELD OF VIEW in the FUV was first proposed in 1986, 20 years ago, on the EURECA platform! (on ground: ASSI table)

• It was then proposed in 1989 for ESA/M2 and was selected for a Phase A on the Space Station (SIMURIS Mission with the Solar Ultraviolet Network, SUN, a 4-telescope non-redundant 2 m baseline array in rotation on the IPS)

• 93: ESA/M3 as MUST/SIMURIS, a 5-telescope circular configuration and, in parallel, was studied for adaptation on the Space Station using an Hexapod support structure

• In 2000, SOLARNET/SPI was proposed for ESA/F2-F3 and recommended by ESTEC review. Even if overcost, the Solar Orbiter was preferred for "political redistribution reasons"

R&D Laboratory Experiments since 1990 on Extended FOV Cophasing and Imaging

• Direct cophasing at /300 of two telescopes on an extended laboratory source in 94

• Fringes and cophasing at /140 on the Sun and /220 on stars and Planets (Jupiter, Mars) in 95 and 96 (Obs. Meudon)

• Stabilities up to /1000 on solar like flux and /100 on mag. 10 stars (ESA/OAST 2 - 1997)

• 2000: acquisition, control and imaging with a 3-telescope cophased breadboard (laboratory setup) with measured stabilities > /300!

SOLARNET R&D Program: Demonstrate Concept and Performances on a Representative Breadboard

• Cophasing & direct imaging in laboratory in 98–2000 (measured /300 phasing)• Adaptation to direct solar observations at Meudon Observatory (Grand Sidérostat de Foucault)

in 2001–2002; completion of guiding and fine pointing this spring (0.1"); cophasing /100 this summer; first images next year (filters & SDM 0.1 nm spectral resolution).

SOLARNET Breadboard: more than 150 optics and detectors!

Big Issues & Next Steps

• R&D– Demonstrate cophased imaging directly on the Sun– Optimize Space Qualification of Fringe Sensor

– Complete integration of Focal Instrument

• Programme– Prepare ESA Cosmic Vision Response (AO expected end of September)

Towards Very High Resolution

An INTERFEROMETER rather than a large telescope:

– Reduced height & mass small platform

&launcher

– Fine Pointing and thermal aspects simplified by small telescopes (use of SiC)

– No need for the complex control of a large primary

– Phasing and pointing the "Perfect" Telescope

1.5 m

1 m UV “Telescope”: 0.02"?: 1 m UV Interferometer: 0.02"

SOLARNET is a Unique Concept of Direct Interferometric Imaging on Extended FOV

• Compact Configuration: 3 telescopes of Ø350mm on 1m

• Spatial Resolution of 0.025” (20–30km on the Sun in the UV)

• Multi-wavelengths spectral imaging 110–400nm with a subtractive double monochromator FUV & UV, coupled to an IFTS 0.002nm

Schematic of SOLARNET Breadboard

Phase measure

Cophasing in Practice

Recombination (in pupil plane on a 1mmRecombination (in pupil plane on a 1mm22 diode) of the 3 beams diode) of the 3 beamsin 2 of the reference interferometers after spatial filteringin 2 of the reference interferometers after spatial filtering

Delay Line

i

i

Modulation Delay Line

i

Cophasing by Double Synchronous

Detection(global WL phase shift)

• 1f provides the error(zeroing method)

• 2f gives the amplitude

Modulation

Delay Line

Recombining Cubes

Photodiodes

White LightInterferogram

Single FrequencyDemodulation

Double Frequency Demodulation

Extended Source - WL - Spatial Filtering

Photodiode

Entrance optics Diameter: L

∫ ⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛ +−ℜ+∗= β

βδπββδ

,..)(

2exp1).,().,)(()( ddh

jeSffdisqPSFI

T

Filtering HolesDiameter: T

h

4 m

Phase Measure Spatial Filtering

With an extented source a spatial filtering is required to measure a proper contrast

Simulation of the interference figure in the case of a contrasted image (granulation – not WL)

Principle of a Spatial Filtering

1.7%

Selection Hole

Microscopeobjective

Image Filtered image

Visibility Ø5µØ10µØ20µ

FOV Centering and Bias

base 1-2

base 1-3base 2-3

High ContrastFiltered Source 1 2

3

OPD (µm)

Contrast (%)

δ1 δ2 δ3

QuickTime™ et undécompresseur

sont requis pour visionner cette image.

Reference FOV and Spatial Filtering

A small decentering of the reference field small)in the baseline direction will produce a bias in the WLF absolute nulling OPD position of δ ~ h. When the intensity distribution is centered (SYMETRY for the 3 baselines), the contrast is maximum on the 3 interferometers and bias is null.

Extreme - highly structured - source in

the reduced FOV after filtering

QuickTime™ et undécompresseur sont requis pour visionner cette image.

1 2

3

Automatic Bias Servo

• Decentering of the intensity centroïd (barycenter) of the reference field of view creates in each of the three reference interferometers a "bias" compared to zero OPD.

• The two major delay lines "monitor" the phase error for B12 and B13 compared to T1 corrections and ∂12 and ∂13 available

• The 3d measurement provides the "differential bias" between T2 and T3; it indicates the vertical offset pointing correction

• The 2f demodulations of B21, B31 and B32 give the amplitudes; they lower with a bias; the closure error (instrumental) gives the residual horizontal correction (since vertical addressed)

• Initial centering and gains are set by initial synchronous demodulation phase measure by jiggling the three active mirrors

This is a multiple servo-control system as we love them!

1 2

3

Permanent Implementation

• If the jitter is implemented on the entrance hole of the spatial filtering (e.g. at 1 KHz) by the focusing objective, the demodulation of the field centering effect (if any) can be very fast and permanent

• Shortage of CNES R&D funds this year (up to now) did not allow to test the method (require object masks, improvement of the 3d interferometer electronics and 2 other synchronous detections)

• We are confident on the approach, useful and fast for Earth Observation (but probably unnecessary on the Sun: reduced contrast and structuration in WL)

Miniaturization of the Reference Interferometers (Phase Measure)

From a breadboard more than a meter long…

… to a 15 centimeters block!

1500 mm

1100

mm

The Interferometric Binding Block of3 Reference Interferometers

• It has been designed and realized• Molecular binding

• 15 Homosil prisms to sub-µm & sub-arcsec precision

• Invar support designed (IDEAS modeling: 0.8 MPA and 2"

for ± 5° tolerance) and awaiting realization (test this autumn?)

R&D Status

• R&D is necessary prior to accepted project to validate hard points and consolidate mission profile so as to prepare competitive response with SCIENTIFIC and TECHNICAL original content

• We have more than 20 years of experience with fringes stabili-zation by synchronous detection (simple and double and, now, with controlled optimization of selective spatial filtering) - and, among them, 10 on the phasing for true imaging on a large FOV

• We have developed an optimum technique to phase multiple telescopes on the SAME extended FOV, even is contrasted and mobile (scanned)

It is more than appropriate to pursue the effort

Conclusions & Perspectives

• We have demonstrated 3-telescope cophasing and imaging in laboratory and we expect to extend the demonstration to the Sun this summer

• Both acquisition and tracking are monitored by our method, and the three levels of servo-control are smoothly interacting: guiding of Siderostat (Platform), fine pointing and optimized cophasing on a self referenced external extended source

• Extension to Earth Observation (LEO or GEO) is straightforward since acquisition and tracking on an Extended source in White Light are similar to the Solar case. Further, a 5 x Ø2 m circular configuration would fit an Ariane V…

This Very High Resolution Interferometry Mission would be possible NOW for a launch in 2012 (as a CNES minisatellite) for the next solar

maximum or in 2016 (Cosmic Vision Proposal) in complement or replacement of SO. EU, US, Indian

and Chinese contributions are discussed.

Thank you!J.-F. HochedezDavid BerghmansFrédéric CletteSteven Dewitte

Werner CurdtEckart Marsch

Volker Bothmer

Richard Harrison

S. Turck-Chieze

Patrick BoumierTahar Amari

Brigitte SchmiederJ.M. MalherbeGuillaume AulanierPascal Démoulin

Silvano Fineschi

J. Trujillo-Bueno

James KlimchukAngelos Vourlidas

Ted Tarbell

Philippe Lamy

Serge Koutchmy

Eric QuémeraisRosine Lallement

Siraj Hasan

Guoxiang Ai