EAGLE

Active Optics Components

E.Hugot - M.Ferrari

Target Acquisition WorkshopParis 11/07/2007

1-Active Beam Steering Mirrors

2-Variable Curvature Mirrors

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 toDeformation proportional to rr22cos (2cos (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 Avoid rotation of the whole BSMBSM• FEM simulations already doneFEM 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 160over(~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:VCM1:Diameter : 60mmRadius of curvature: 1491 mm à 1192 mmFocal ratio range: 12.5 à 9.5Sag variation : 75 m 

VCM2:VCM2: Diameter : 20mmRadius of curvature: 102 mm à 87 mmFocal ratio range: 2.55 à 2.15Sag variation : 84 m

Optical quality : /10 rms (tbc) 1.5m

Variable Curvature Mirrors

Goal and Specs:

87 1021192 1491

Ø = 60mm F/D 12.5 9.575m sag

Ø = 20mm F/D 2.55 2.1584m sag

EAGLE VCMs

84mm 2800mm Ø = 16mm

F/D 90 2.4380m sag

VLTI VCMs

Variable Curvature Mirrors

Comparison with existing systems:

Fine positionning of UT/AT pupilsin the VLTI recombinaison lab.

Optical surface quality:/4 (HeNe) over full range

DL Cat’s Eye M3 active mirror

16 < Dinput < 250m 24 < Doutput < 85m

Rc varying from 2800 to 84mm

Variable Curvature Mirrors

VLTI Delay Lines:

• Six Delay-Lines equiped since 2002

8 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 laboratoryControl accuracy 0.5 mbar over 0-10 bar range (5.10 -5)

Telescope pupil positioning accuracy Telescope pupil positioning accuracy (in interfero lab)(in interfero lab) < 15cm over < 15cm over 350 m350 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 – ESOVLTI 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 statusToday status::5 VCMs delivered to ESO for first 2 ATs Integration in PRIMA StS - 2007

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 6273-102 (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 3273-177 (2006)

• Ferrari M. et al, “Development of a Variable curvature mirror for the delay-lines of the VLT Interferometer”, Astronomy & Astrophysics Sup. Ser., 128; 221-227

• 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 6273-71 (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