Roberto RagazzoniINAF – Astronomical Observatory of Padovaroberto.ragazzoni@inaf.it

Feasibility of the aspheric lensCatania, June 11 2014

On behalf and with extensive inputs from the Telescope Group (D. Magrin, D. Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto, M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U.

Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti)

Roberto RagazzoniINAF – Astronomical Observatory of Padovaroberto.ragazzoni@inaf.it

Feasibility of the aspheric lensCatania, June 11 2014

On behalf and with extensive inputs from the Telescope Group (D. Magrin, D. Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto, M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U.

Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti)

This is still the “old” PLATO 1.0 group

The aspheric issue…

We have been asphericized by an hard life (thank you Silvio…)

We had two offers from manufacturer for actually making one (in S-FPL51) for test (SESO & Silo)

We have a detailed plan and feasibility by Sagem-Reosc that already manufactured two similar sets for a different space project (and they made similar comments as Zeiss quotation in RUAG report!)

ESA challenged themselves to improve Thales design to achieve performances and found they need two aspherics

Asphere is on a lens with one flat surface MediaLario is testing their manufacturing

abilities on glass S-FPL51

From a summarizing slide of June 15, 2011 (3 yers ago…)

The aspheric issue…

We have been asphericized by an hard life (thank you Silvio…)

We had two offers from manufacturer for actually making one (in S-FPL51) for test (SESO & Silo)

We have a detailed plan and feasibility by Sagem-Reosc that already manufactured two similar sets for a different space project (and they made similar comments as Zeiss quotation in RUAG report!)

ESA challenged themselves to improve Thales design to achieve performances and found they need two aspherics

Asphere is on a lens with one flat surface MediaLario is testing their manufacturing

abilities on glass S-FPL51

From a summarizing slide of June 15, 2011 (3 yers ago…)

The team background

Rosetta Wide Angle Camera design An off-axis tilted FoV design with

aspheric mirrors Emphasys was on detection of faint

gasesous features from comet nuclei Clean PSF: unobstructed pupil,

monochromatic and low scatter designNone of the above does apply to

PLATO!Several ground based 4m and 8m

class instruments (all with aspheric surfaces)

Postcards sent around…

Postcards sent around…

Two of the lens has an aspheric surface

surprisingly similar in size and deviation!

Impact of increasing aperture & FOV on Thales optical design for Plato.

January 2010Isabel Escudero

Purpose of study.

Modify Thales design as follows: Entrance aperture diameter: 15% bigger. FOV: from a circle of 28º diameter to a

square of 28º side length. Image: quality equivalent to that of

Thales design for the whole new FOV (criterion is 90% EEC diameter)

Focal length: same as original Add Fused Silica plate in front Aspherics necessary?

Comparing sizes.10:01:23

plato_thales ME 11-Jan-10

50.00 MM

10:11:01

Science 15-Jan-10

50.00 MM

15:48:36

plato_v10 ME 08-Jan-10

50.00 MM

15:49:37

plato_v20 ME 08-Jan-10

50.00 MM

Thales Science

Plato_v10 Plato_v20

Comparing performance

Design Field object (degrees) Diameter of 90% encircled energy (µm) Plato_Thales Axis/9.6/13.7º/19.6º 34.8 / 42.6 / 58.9 / NA Plato_v10 Axis/9.6/13.7º/19.6º 39.7 / 34.4 / 41.8 / 65.8 Plato_v20 Axis/9.6/13.7º/19.6º 31.9 / 34.0 / 42.8 / 59.6

System EPD (mm) EFL(mm) FOV Thales 83 239.5 28º diameter circle Science 120 247.5 28º diameter circle Plato_v10/Plato_v20 95.45 239.5 28º side square

Design Field Object Incidence Angle at image Distortion (%) Plato_Thales 14º 26.7º 0.7 Plato_v10 19.6º 38.3º 0.7 Plato_v20 19.6º 38º 2.0 Science 14º 31º 2.9

Conclusions: Thales_v10/_v20.

Two aspheric surfaces are required for larger EP & FOV.

If FOV = 28º diameter circle, one aspheric surface is enough.

Fused silica plate becomes a lens: curvatures and aspheric are needed.

Note values of distortion (=> calibration and post-processing for field superposition).

Note large angles of edge field object at image plane: relevant for radiometry.

Conclusion by ESA…

Do we need aspheres…?

Yes… Accordingly to ESA (upgrading of THALES design)

at least two; With our own design (actually all the “last”

versions) just one.

Feasibility strategy

ESA never questioned feasibility of one TOU

ESA often being concern about “mass” (well, sort of…) production

Construction is one of the issues..We focus on demonstrating a fast

procedure (less than one week) in the warm…

Aggressive plan to demonstrate we can handle CaF optical elements

Frame connected to the bench, allowing the rotation for lenses insertion from the top and their alignment similarly to what would happen with the final structure, withthe possibility to be rotated of 180º to insertthe lenses from both sides(L3 will be the first one)

TOU BreadBoard

Rotating points

TOU Dummy Structure

Laser

Beam Expander

Iris1

B/S

Back Reflected Light

Transmitted Light

CC

D

CCD

Iris2

Alternative designs

A design with an aspheric CaF (because SESO claimed that with some manufacturing process that would be easier/cheaper/faster)

A design CaF-free (in case we fail space qualification of CaF lens)

A design taking into account the common directives of manufacturer

Design 4

BK7 G18CaF2

CaF2N-KZFS11 S-FPL53 KZFSN5

BK7

Design 4 - EE

90%EE<30×30 arcsec2 ~ 2×2 pixels2

90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2

90%EE<45×45 arcsec2 ~ 3×3 pixels2

2×2 pixels2

Design 5

BK7 G18S-FPL51

N-KZFS11S-FPL53 KZFSN5

BK7

S-FPL51

Design 5 - EE

2×2 pixels2

90%EE<30×30 arcsec2 ~ 2×2 pixels2

90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2

90%EE<45×45 arcsec2 ~ 3×3 pixels2

Baseline - EE

90%EE<30×30 arcsec2 ~ 2×2 pixels2

90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2

90%EE<45×45 arcsec2 ~ 3×3 pixels2

The CaF issue…

Already flown… One company (SESO) would prefer as

asphere Baseline design has CaF in the spherical,

smallest and more protected position (L3) We have in our hand a produced L3

identical to the flight one (assuming baseline)

We have two blanks similar in size, glued to the same holder and cured in two different ways now in CNES and UniBern for thermal and vibration tests…

We have an acceptable, although not brilliant, B plan CaF-less

Foreseen Activities (CaF2):

Shipped blank to PD

Shipped to SGGluing blankCuring (th.cycle)Shipped to PDShipped to UniBEVibratingShipped to CNESThermal cycling

Shipped blank to PD

Shipped to SGGluing blankShipped to PDShipped to CNESThermal cycling

Survived!

Survived!

Remember that L3 in the BB

is made in CaF2 as well!

Foreseen Activities (BB):

Mounting lenses on mounts (gluing) Aligning within tolerances Testing the “warm” optical quality

interferometrically Measuring the “warm” PSF directly Measuring the “warm” PSF via Hartmann Measuring the “cold” PSF directly Measuring the “cold” PSF via Hartmann Validation or lessons learned of the

alignment process

DONE !!!

One aspheric done on purpose…

Various studies issued…

Various studies issued…

Production plans…

Production plans…

Production plans…

Summary…Selex: Ok with industrial planSagem/Reosc: Ok with industrial planMediaLario: Interested, feasibility Ok, now joining

Selex?Seso: Ok but would prefer CaF2 (technology driven)RUAG: Market analysis…

Zeiss: doable, delivery time non critical

Asphericon: doable at the limit (delivery time) of their abilities

Steinbeis TransferZentrum: identified several technologies

Leica: doable, but reccomending harder material Fisba: they do not have capabilities (in spite of…)

PrazisionOptik: they do not make aspheres

SwissOptics: they think are doable but exceed the size they handle

What is next…?

Regain informal contact with all industries (some already made on their own… Sagem & MediaLario)

Select one or two for an updated formal adjourned contact

Place the accent on the serial and industrial production

Take –very fastly- a final choice as the overall baseline based on existing informations