EAGLE Active Optics Components E.Hugot - M.Ferrari Target Acquisition Workshop Paris 11/07/2007

1-Active Beam Steering Mirrors 2-Variable Curvature Mirrors

Active Beam Steering Mirrors Diameter : 100mm Radius of curvature: 1803mm Able to provide strong Astigmatism compensation Range:  Up to 100 µm PtV of Astm compensation Goal and Specs: Astm deformation obtained from Finite Element Analysis (courtesy P.Vola)

Active Beam Steering Mirrors The concept: Two pairs of opposite forces applied on a vase form mirror: –internal meniscus = Optical surface, –Thick external ring = location of forces, far from the optical surface. Two thickness distributions: –Radial thickness distribution –Angular thickness distribution Deformation proportional to r 2 cos (2  ). Deformation proportional to r 2 cos (2  ).

Active Beam Steering Mirrors Perspective view: Possibility of Focus compensation over a range of 10 µm PtV

Specific profiles Central fixed clamp Polishing tool Polishing under going at LAM Active Beam Steering Mirrors The prototype:

Smart Beam Steering Mirrors 4 forces = 1 actuator The concept: Avoid rotation of the whole BSM Avoid rotation of the whole BSM FEM simulations already done FEM simulations already done The extension: 8 forces = 2 actuators 1 mode 2 modes Rotation of the Astm deformation mode

€ Smart Beam Steering Mirrors Advantages: 1.Simplification of the Command/Control system 2.Simplification of the calibration 3.Reduces the weight of the overall system 4.No parasite Tip/Tilt errors 5.Better thermal behaviour 6.Better reliability 7.Gain in money

Smart Beam Steering Mirrors Only 1 point of actuation Optical quality of the deformation  160  over  (~6µm) First demonstration:

FEM simulation done First prototype manufactured (4 forces design) Performances under evaluation (F. Madec) Smart BSM concept proven Next prototype (2 forces) under finalisation Based on mature technique Status: Active/Smart Beam Steering Mirrors

1-Active Beam Steering Mirrors 2-Variable Curvature Mirrors

VCM1: Diameter : 60mm Radius of curvature: 1491 mm à 1192 mm Focal ratio range: 12.5 à 9.5 Sag variation : 75  m VCM2: Diameter : 20mm Radius of curvature: 102 mm à 87 mm Focal ratio range: 2.55 à 2.15 Sag variation : 84  m Optical quality : /10 rms (tbc)  1.5  m Variable Curvature Mirrors Goal and Specs:

Ø = 60mm F/D 12.5   m sag Ø = 20mm F/D 2.55   m sag EAGLE VCMs 84mm 2800mm Ø = 16mm F/D 90   m sag VLTI VCMs Variable Curvature Mirrors Comparison with existing systems:

Fine positionning of UT/AT pupils in the VLTI recombinaison lab. Optical surface quality: /4 (HeNe) over full range DL Cat’s Eye M3 active mirror 16 < D input < 250m 24 < D output < 85m R c varying from 2800 to 84mm Variable Curvature Mirrors VLTI Delay Lines:

Six Delay-Lines equiped since VCMs delivered to ESO (6 DLs + 2 spares) Open loop + initial calibration Variable Curvature Mirrors

Designed to work on Open-loop Computer embedded on the delay line (low power consumption) Operating system and control- command programs stored on flash disk Infrared serial line to the LCU Two pressure gages connected to the computer by classical RS232 Variable Curvature Mirrors Control/Command: Piston Over Pressure Chamber Front End Processor

Over Pressure Chamber & Front End Processor Systems installed on VLTI DLs carriages  Low power consumption < 15 W Variable Curvature Mirrors

Open-loop operation: Analytical model for Rc = f(P) Includes effect of hysteresis (mirror material parameters) Pressure/Curvature initial calibration in laboratory Control accuracy 0.5 mbar over 0-10 bar range ( ) Telescope pupil positioning accuracy (in interfero lab) < 15cm over 350 m Hysteresis pressure effect in the increasing/ decreasing cycles for the range [0, Pmax] (Pmax = 7, 6, 5,....1 bar) Variable Curvature Mirrors Open loop / Hysteresis calibration

2006 : VCM integration on DLs n°5 & 6: - Mask located at UT Coudé - DL carriage position from 5 to 55m (OPL 10 to 110m ) - Imaging at Interferometric Lab (MIDI location) 24m < Total OPL < 134 m Variable Curvature Mirrors Pupil re-imaging test:

J moon in IRIS Fwhm = 7.6 arcsec A bit of J band Moon observed in August with AT2 through DL6, after installation of the VCM. Without VCM, the Delay Line do not relay the exit pupil at the entrance pupil of the VLTI lab, at the cost of a FoV limitation. In extreme AT situations, the FoV diameter can even be smaller than the FWHM of the MIDI diffraction limited PSF. The transmitted FoV after VCM integration has been measured to ~8 arcsec up to OPL larger than 100m. Henri Bonnet – ESO VLTI Task Force Variable Curvature Mirrors

VLTI Delay Lines Variable Curvature Mirrors

Dual Field for phase reference imaging. (bright reference star and faint object) Need to transfert 2 independent fields from AT stations to DL tunnel. Stars Separator located at AT Coudé train  2 VCM systems per AT Today status: 5 VCMs delivered to ESO for first 2 ATs Integration in PRIMA StS ESO ordered 5 more VCMs systems for ATs n° 3 & 4. (PRIMA with 4 ATs) Variable Curvature Mirrors VLTI PRIMA Stars Separators:

VCMs Variable Curvature Mirrors VLTI PRIMA Stars Separators:

Existing mature systems Already installed at ESO instrument level More than 12 systems in VLT/VLTI Fully operational in ESO software environment One VCM working at GI2T for ~ 10 years Variable Curvature Mirrors Status:

References Lemaitre G., "New method for making Schmidt corrector plates", Applied Optics, vol.11, n°7, p.1630 Nelson J. et al, " 1. Stressed mirror polishing, a technique for producing nonaxisymmettric mirrors", Applied Optics, vol.13, n°14, 2332 Hugot E. Lemaitre G. Ferrari M., "Toric mirrors and Active Optics: degenerated configuration for spherical monomode deformable mirrors“, SPIE Proc. on Astronomical Telescopes and Instrumentation, Paper number (2006) Hugot E. Ferrari M., “Active polishing of a 2mm Thin Shell for large adaptive secondary mirrors”, SPIE Proc. on Astronomical Telescopes and Instrumentation, Paper number (2006) Ferrari M. et al, “Development of a Variable curvature mirror for the delay- lines of the VLT Interferometer”, Astronomy & Astrophysics Sup. Ser., 128; Madec F., Hugot E., Ferrari M., “New beam steering mirror concept and metrology system for multi-IFU", SPIE Proc. on Astronomical Telescopes and Instrumentation, Paper number (2006) Lemaître et al, 2001, ‘Universal method for holographic grating recording: multimode deformable mirrors generating Clebsh-Zernike polynomials’, Applied Optics, vol. 40, n°4, 461