FLAO Alignment Procedures

G. Brusa, S. Esposito

FLAO system external review, Florence, 30/31 March 2009

FLAO system external review, Florence, 30/31 March 2009 2

FLAO 09 Alignment Procedures

• Test Tower alignment of M2 Unit, Retro-Reflector and W Unit.

• Telescope alignment of M2 Unit, M3, Retro-Reflector and W Unit, for calibration purposes.

• Telescope alignment of W Unit, with de-rotator axis.

FLAO system external review, Florence, 30/31 March 2009 3

Test Tower Setup

• ~13.7 meters of optical (vertical) path.

• Two conjugate configuration

• M2 Unit at top with dummy telescope hub.

• Retro-reflector structure mounted on hub.

• AGW Unit mounted at bottom of tower.

FLAO system external review, Florence, 30/31 March 2009 4

Part A - Description

• M2 Unit, i.e. adaptive secondary, hexapod and hub.

• Retro-reflector support and optics.

F/1 parabola

flat

FLAO system external review, Florence, 30/31 March 2009 5

Part B - Description

• IR camera dichroic

• Beam Splitter

• Internal Calibration Source

•WFS board

FLAO system external review, Florence, 30/31 March 2009 6

Optical Setup

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

x

y

z

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

x

y

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

LBT672

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

to WFS

to LBT672

RR

ICS focus

BS

IRTC entrance window

x

y

z

x

y

z

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

to LBT672

to WFS

From ICS

ICS focus

BS

x

y

x

y

Part A

Part B

FLAO system external review, Florence, 30/31 March 2009 7

Alignment Goals

•The two optical axes (Part A and B) have one point in common: the ICS focal point.

•The two optical axes have a maximum angular offset of <2 arc-min. Limited by de-rotator sensitivity to angular misalignment.

•The total wave-front aberration is not significantly larger than the baseline for the AS figure (120nm RMS). Limited by wave-front sensor range.

FLAO system external review, Florence, 30/31 March 2009 8

Alignment Preliminary Requirements

The alignment of the retro-reflector structure with the AS and the RR has been already carried out during the optical characterization of the AS [AD17]. So that we can rule out large errors in the positioning of the various component of Part A (in particular the retro-reflector).

The W-unit should be internally aligned, using the optical axis of the first lens of the triplet as a reference axis [AD in preparation]. So that we can rule out large errors in the positioning of the various component of Part B.

The AS figure error (WF, single pass) should be ~60nm RMS (flattening baseline) [AD2]. To bring it within the WFS optical aberration range.

FLAO system external review, Florence, 30/31 March 2009 9

Step 0 - Initial configuration

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step1

M2 axis

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step1

M2 axis

IRS

RR

VM2

WFSaxis

step1

M2 axis

• RR positioning error: +/- 2mm

• ICS position: manually adj.

• Hexapod adjustment.• Translation: +/- 5mm• Vertex rotation: +/- 15’

• WFS board adj.• Translation: ~100mm• Tilt: ~15 arcmin

ICS

FLAO system external review, Florence, 30/31 March 2009 10

Step 1 – Auto-collimation

Step 1 is achieved by tilting the AS unit around its vertex (using the Hexapod) until the AS axis is bisecting the angle IRS-VM2-RR.

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step1

M2 axis

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step0

M2 axis

M2 shift& rotation

IRS

RR

VM2

WFSaxis

step1

M2 axis

IRS

RR

VM2

WFSaxis

step1

M2 axis

Vertex rotation

RR-ICS axis RR-ICS axis

ICS ICS

FLAO system external review, Florence, 30/31 March 2009 11

Step 2 – Off axis correction

IRS

RR

VM2

WFSaxis

step1

M2 axis

RR-IRSaxis

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

IRS

RR

VM2

WFSaxis

step1

M2 axis

RR-IRSaxis

IRS

RR

VM2

WFSaxis

step1

M2 axis

RR-IRSaxis

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

Step 2 is achieved by tilting the AS unit around its center of curvature (using the Hexapod) until the AS axis is aligned with the IRS-RR direction.

RR-ICS axis RR-ICS axis

rotation

ICS ICS

FLAO system external review, Florence, 30/31 March 2009 12

Step 3 – WFS pupil centering

IRS

RR

step2

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

IRS

RR

step3

IRS

RR

VM2

WFSaxis

M2 axis

RR-IRSaxis

IRS

RR

step2

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

IRS

RR

step2

IRS

RR

VM2

WFSaxis

step2

M2 axis

RR-IRSaxis

IRS

RR

step3

IRS

RR

VM2

WFSaxis

M2 axis

RR-IRSaxis

IRS

RR

step3

IRS

RR

VM2

WFSaxis

M2 axis

RR-IRSaxis

Step 3 can be achieved by tilting the WFS board with respect to its translation stages.

ICS ICS

RR-ICS axis RR-ICS axis

FLAO system external review, Florence, 30/31 March 2009 13

Summary

1. We have identified an alignment strategy that provides:1. Minimization of the off-axis aberration of M2.2. Alignment of the WFS Unit pupil image.

2. At the test tower the optical axis is identified for by the location of the ICS.

3. At the telescope the identified axis will need to be the de-rotator mechanical axis. The strategy will need to be updated.