“Milliarcsecond imaging in the UV- Optical domains:Preparing the way to space borne Fresnel Imagers”, Nice, 23-25 Sept. 2009

INSTALLING A FRESNEL IMAGERINSTALLING A FRESNEL IMAGER

ON A 122 YEARS OLD REFRACTORON A 122 YEARS OLD REFRACTOR

Jean-Pierre RivetCNRS, Observatoire de la Cote d’Azur

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The 76cm refractor

The 76cm refractor

Available since: 1887Refurbished in: 1966Focal length: 1789 cm @ 546 nmDiameter: 76 cmMount: German equatorialDome diameter: 24 mDome weight: 93 000 kgDesign: Ch. Garnier, G. EiffelRegistered as an historical monumentStill active scientifically...

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Why on this instrument ?

The 76 cm refractor in Nice is:• an 18 meters-long optical bench (no beam folding required),

• on an equatorial mount,

• easily available,

• with local scientific and technical environment.

18 m

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The drawbacks

• Less than ideal celestial tracking

• Seeing conditions

• Light pollution

• No build-in automatic guiding available

• Tube flexions

• Constraints due to the status of historical monument

• modifications forbidden on genuine parts

• only fully reversible actions allowed

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The mechanical layoutof prototype “Generation 1.5”

Milestones:• Prototype Generation 1 laboratory testbed, Toulouse, 2008• Prototype Generation 1.5 first on-sky experiment, Nice, July 2009• Prototype Generation 2 fully featured on-sky testbed, Nice, October 2009 ?

Optical rail(field optics, 0th order mask,correctors, cameras)

18 m refractor tube

Fresnel array

76 cm objective lensNot toscale !

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The optical rail

Field optics(Maksutov)

Optical rail(2 meters)

Imagingdoublet

16 mm BlazedFresnel lens

Zero ordermask

2-axis forkmount

CCD CameraSXVH9 (1)

Flipmirror

XY motorizedlinear stages

Link torefractor tube

Link torefractor tube

Not toscale !

Baffles

(1) Starlight Express CCD Camera 13921040 pixels of 6.45m.Sensor: Framos ICX285

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The Fresnel array

Laser-machined Copper-Beryllium blade20cm 20 cm; 700 Fresnel zones (on the ½ diagonal)

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The Fresnel array

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Reversible bindings

• The Fresnel Imager is attached to the refractor tube

in a fully reversible way:

Refractor tube

Steel strip

Stay tensioners

Shackles

Fresnel imager mount

Felt soles

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Fork mount for the optical rail

• The optical rail’s orientation can be fine-tuned for optimal

chromatism correction:

Link to the refractor tube

Two-axis fork mount

Auxiliary refractor (finder)

Refractor tube

Safety steel strip

Optical rail

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Remote-controlled chromatism correction

• The optical rail orientation with respect to the Fresnel array

can be remote-controlled, to compensate for tube flexions

Flexible copper plate

Connection pin

Motorized linear stages (X, Y)

Link to the refractor tube

Optical rail

Optical rail interface

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Towards “Generation 2” testbed

• Full-size blazed Fresnel lens (diameter = 58 mm instead of 16 mm)

available, integrated; to be tested on-sky

• “Andor Lucas R” science and guiding EMCCD cameras

(10041002 8m pixels), with dedicated software

to be delivered soon

• 100 Hz tip-tilt corrector

lab tested; to be integrated and tested on-sky

• New generation refractor’s slow motion keypad (computer-driven)

available, integrated; to be tested on-sky

• Flexion compensators for the optical rail

to be integrated and tested on-sky

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Expected completion date: November 2009

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58mm blazed Fresnel lens

• Diameter: 58 mm

• Number of zones: 696

• Substrate: Fused silica

TO BE TESTED ON SKY

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100 Hz tip-tilt corrector

• The imaging doublet is mounted on XY piezo translator, driven

by a guiding camera, through a 100 Hz computer-based servo-loop,

for real-time correction of turbulent tip-tilt, tube flexion, and

celestial tracking defects.

• Refractor’s slow motion keypad modified to be computer-driven

Mechanical support

XY piezo translator(replaced by a fake aluminium parton this image)

Imaging doublet

TO BE TESTED ON SKY

C1

Thank you for your attention !