September 28, 2007 LGS for SAM – PDR – Optics 1

LGS for SAMLGS for SAMOptical AlignmentOptical Alignment

R.Tighe, A.Tokovinin.

LGS for SAM Design Review September 2007, La Serena

September 28, 2007 LGS for SAM – PDR – Optics 2

Flexure measurements of SOAR

IR Nasmyth Optical

Nasmyth

Laser Box on one of the serrurier trusses at bent-cass port #2 at 45Deg from IR Nasmyth.

Note: As shown in SAM SDN; SAM-AD-02-6301 (SOAR flexure measurements), the flexure seems due to elevation ring sag. Mounting the laser box on the truss should decrease the effect. So the expected flexure is less than the above values.

Beam Transfer

Laser Launch Telescope

The SOAR Maximum Flexure (Top Ring w/r to Elevation Ring):

(Top Ring w/r to Optical Axis):

Displacement [Y]≈ 2mm.

Tilt [x] ≈ 1 Arcmin.

Tilt [x] ≈ 20” (5” corr.ON).

September 28, 2007 LGS for SAM – PDR – Optics 3

The Laser-Box Alignment

~1.5m

Alignment Mirrors Am1&Am2 (coating450-700nm)

Blue Laser

UV Laser

Co-align UV and Blue Lasers, e.g. by center and auto-collimation from a distant target (~10m) or any other method, Laboratory work.

~10m

September 28, 2007 LGS for SAM – PDR – Optics 4

Beam Transfer

The LGS beam transfer Adjustments(Alignment done with the blue laser)

LLT

IR

m4

m3

SOAR Elevation Ring

The Laser Box Adjustments:

Tilts: x=±0.5º; y=±0.5º.

Target on m4.

The m4 Adjustments:

Active Tilts: x=±2º; y=±2º.

Target on LLT entrance.

The m3 Adjustments:

Tilts: x=±2º; y=±2º.

Auto-collimation back to Laser.

September 28, 2007 LGS for SAM – PDR – Optics 5

The LLT Alignment

Step 1: The general procedure:

Center and Auto-collimate from LLTm2.

X-Y (and Z) displacement of LLTm1 until the foci of both mirrors are coincident.

Tip-Tilt LLTm1 pivoting around the common focal point, until beam is centered in LLTm1.

The active tip-tilt of m4 will keep the beam centered on LLTm2 (and LLTm1) and therefore IQ stays coma free up to ~1º of LLT pointing correction (need < 1’).

LLTm1

LLTm2

LLTm2 Center of curvature

LLTm2 focus

LLTm1focus

September 28, 2007 LGS for SAM – PDR – Optics 6

8mm parallel beam only Center Field

485mm

Step 0: The general procedure.

Center and Auto-collimate from LLTm2.

Re-center (or tilt) LLTm1 to make both mirrors’ foci coincident.

The LLT Alignment

Step 2: In the Laboratory:

The auto-collimated beam (into CCD or back to Laser) is measured with a WFS.

September 28, 2007 LGS for SAM – PDR – Optics 7

The LLT Alignment

Step 3: 1rst Pointing Alignment.

The Optical Axes of the LLT and SOAR telescope are made coincident by Tip-Tilting the LLT as a whole (daytime).

September 28, 2007 LGS for SAM – PDR – Optics 8

The LLT AlignmentStep 4: 2nd Pointing Alignment and m3 Adjustment.

The Optical Axes of the LLT and SOAR telescope are fine tuned with a Star image and m3 is adjusted to mount LLT onto the beam transfer optics.

Image the star in the predefined position

on the LLT alignment & pointing CCD

camera.

The Pointing Tuning:

The m3 final Adjustment:

Two checks:1) Laser auto-

collimation (flat mirror on LLT).

2) Star image in CCD-

camera at m4 or at

laser box.

September 28, 2007 LGS for SAM – PDR – Optics 9

The LGS beam Control

UV

VIS

Soleil-Babinet Compensator

8x Beam Expander

Beam Profiler CCD

355nm Tripled Nd:Yag Laser

355nm laser-line Dump switch-Mirror

Alignment Mirrors Am1&Am2 (coating450-700nm )

Beam Dump / Power meter

Blue Alignment Laser (473nm)(or better400-420nm?)

8mm Gaussian Beam Exit Window

Intra-cavity Shutter

~1.5m

Laser GB quality control:

Power Check replacing beam-dump with power-meter. Also a photodiode checks the LLT outgoing beam.

M² check with Beam profiler.

GB centering on LLTm2:

By 4 photodiodes at the edge of LLTm1.

LGS quality control:

Flux return and spot size in the LGS WFS.

LLT alignment control:

Donut (or defocused star) image on LLT alignment/pointing CCD camera.

September 28, 2007 LGS for SAM – PDR – Optics 10

Experiments and To Do List

Experiments:

Test the Beam-Expander. Parallel beam and waist image formation as well as chromatic focus differences.

Test the S-B compensator and measure phase shifts.

Test the Beam profiler and Power meter. Calibrate photodiodes.

To Do:

Purchase the Laser-Box and beam transfer optics.

Refine the LLT Opto-mechanical design and do the optical procurement.