Gabby Kroes Lars Venema, Ramón Navarro ICSO 2012 AJACCIO GABBY KROES PAPER 0013

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1 Gabby Kroes Lars Venema, Ramón Navarro

2 CONTENT Issues cryogenic transmission optics mounts Concepts Compensation mount Ground based application examples

3 INSTRUMENTATION FOR INFRA RED Instrumental background reduction by cooling For MID IR down to K Various environments Ambient: production/integration Cryo: operational circumstances Ambient/cryo: transport/launch CTE mismatch (Δx up to mm/m) Structure high CTE (Alu) Optics low CTE (CaF2, GE, ZnSe, Infrasil etc.)

4 Firmly fixing OPTICS MOUNTING Mechanical stability, accurate positioning under test and operational circumstances No (low) stresses Deformations, birefringence, breakage

5 REQUIREMENTS Accurate positioning in test and operational environments (changing gravity) No (low) stresses within the optics Survive launch/transport environment Adjustment free Simple optics geometry Accessibility of refs during manufacturing Good heat conductance Limited number of (additional) components Detachable not bonded optics

6 RADIAL SUPPORT V block De centre between temp. regimes High spring load Kinematic springs Connect (integrate) to optic High spring load CTE compensation Accurate alignment at 2 temp. regimes No (low) loads

7 No bonding BONDING High spring rates to avoid sagging High deformation Bonding No sagging lower springrates Accurate glue spot sizing Detailed knowledge glue properties Stresses due to glue (CTE mismatch)

8 GLUE EFFECTS Delamination expected Chunks of optics broken away

9 AXIAL LOCATION OF RADIAL SUPPORTS In centre of lens Additional deformation effects In bulk of lens Stresses are guided through the bulk of material

10 AXIAL SUPPORT Spring Press opposite axial support points Oversizing in case of birefringe CTE compensation

11 NUMBER OF SUPPORT POINTS 176 mm diameter CaF2 lens 3 points Larger deformation; 3.83 nm PV Unwanted surface shape Sagging risk 6 points Smaller deformation; 2.04 nm PV More preferred surface shape

12 CTE COMPENSATION MOUNT Δx between Alu and lens compensated with CTE pads Structure: Alu (!) CTE pads: thermo elastic plastic CTE > Al (e.g. POM) > CTE = < pads Dedicated CTE pads for each lens material and dimensions

13 ISOSTATIC POINT (SHRINKAGE CENTRE)

14 LAUNCH 60 G Static load σ cover = 24 MPa σ lens = 2 MPa 1st mode = 3105 Hz

15 SPIFFI 2K CAMERA SPectrograph for Infrared Faint Field Imaging (SPIFFI) 2K camera. Part of the SINFONI instrument for the Very Large Telescope (VLT) in Chili. Cassegrain focus; varying gravity loading Wavelength range λ: 1.1µm to 2.45µm Operating temperature is 77K

16 OPTICAL DESIGN Size [mm] L1 Ø 176 L2 Ø 172 L3 Ø 172 Mirror NA L4 Ø 88 L5 Ø 88

17 REQUIREMENTS Image position within 0.1 pixel Image motion < 1.8 μm Lens requirements Position [μm] Tilt [ ] Tilt [mrad] Initial stability Initial stability Initial stability L L L

18 TRIPLET

19 CTE/MANUFACTURING ERROR L1 ( ) 1.4 nm L2 ( ) 1.9 nm L3 ( ) 8.3 nm Additional tuning

20 THERMO ELASTIC EFFECT Three point thermal coupling 18 K 24 W/h cool down ( ) σ = 8.2 MPa

21 ACCURACY Lens is referenced to the outer circumference of the mount Higher manufacturing accuracy Via the CTE pads Lens dimensions Accurate round lens necessary Accurate (axial) support planes Precise dimensions to be determined after manufacturing

22 TRIPLET

23 ICSO 2012 AJACCIO GABBY KROES PAPER 0013

24 X SHOOTER Dimensions [mm] Material Base Plane Height Prism I Infrasil 160x160x Prism II ZnSe 140x140x Prism III ZnSe 129x129x52 135

26 CONCLUSIONS Succesfull application of compensation mounts in groundbased instrumentation Stringent positional and stiffness requirements Accurate at ambient and operational circumstances Play free mounting under all circumstances Next step: Launch qualification FEA shows save grasping of lens by the mount No optical requirements during launch Higher allowable stresses and positional errors Warm and even cold launch feasible Adjustment free cryogenic space instrumentation

27 END Thanks for your attention

28 THERMAL CONNECTION X shooter corrector lens Additionla copper braids to lens circumference

29 ASSEMBLY Measure lens diameter Determine hard stop dimensions Mount CTE pads Position accurate hard stops (referenced to flat surfaces at holder circumference) Determine torque for CTE pads Mount 3 CTE pads Replace hard stops with CTE pads Mount cover

30 CTE VALUES

35 SURFACE SHAPE ACCURACY Fringes at λ = 633 nm Radius important PV for FEA

Mounting of large lenses in Infrared instruments

Mounting of large lenses in Infrared instruments Jean Louis Lizon, Gotthard Huster European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany ABSTRACT Infrared instruments