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

LGS for SAMLGS for SAMOptical DesignOptical Design

R.Tighe, A.Tokovinin.

LGS for SAM Design Review September 2007, La Serena

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

IR Nasmyth Optical

Nasmyth

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

Note: a 7m long Laser umbilical cable has been tested. It can be laid out from the base of the truss directly onto the IR-Nasmyth cable-wrap mobile section passing over the elevation bearing and reaching the pillow-block (next picture).

Working solution:Laser control

and cooler position (on the ledge at the IR Nasmyth pillow-

block level).Beam Transfer

Laser Launch Telescope

The LGS System on SOAR

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

The Laser umbilical cable handling on SOAR

The Laser control & Cooler Rack.

Cable length = 7m.

Laser cable layout fit-test (yellow line).

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

truss

IR Nasmyth

Focus

Cable-wrap; mobile

Cable-wrap;static

Yellow line is the 7m Laser

Umbilical Cable Layout

Rack for laser control, power and Cooler at pillow-block level

Laser Cable and Rack at IR-Nasmyth

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

LLT

IR

m4

m3

Laser Box

SOAR Elevation Ring

The LGS system (GB propagation)

Requirements:

LLTm1: R=1000mm, =300mm (pupil).

GB 1/e² diameter footprint on LLTm1=260mm.

Decided:

LLTm2: R=30mm, =15mm.

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

Laser-Box

UV

VIS

Soleil-BabinetCompensator

8x Beam Expander

Beam Profiler CCD

355nm Tripled Nd:Yag Laser

355nm laser-line Dump switch-Mirror

Alignment Mirrors Am1&Am2 (coating450-700nm )

UV Laser Beam Dump

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

8mm Gaussian Beam Exit Window

Intra-cavity Shutter

LLT

Laser Launch Telescope Beam Transfer

The LGS system

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

The optimized LLT:

LLTm1:

Diameter(mm) Radius(mm) Conic

300 1000 -0.99979

LLTm2:

Diameter(mm) Radius(mm) Conic

15 15 -1.00001

485mm

LLT

30Arcsec Field (on sky)

13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively.

The Laser Launch Telescope

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

485mm

LLT

30Arcsec Field (on sky)

13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively.

OPDComa=57nmOPD rms = 59nmOPD p-v =115nmStrehl Ratio= 0.88

Comatic PSF

The working LLT:

LLTm1 (pivots around center of curvature of LLTm2):

Diameter(mm) Radius(mm) Conic

300 1000 -0.9702

LLTm2:

Diameter(mm) Radius(mm) Conic

15 15 -0.0

The Laser Launch Telescope

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

The Laser-Box

The S-B compensator (UV):

8-500-UV-25 (10) from Special Optics

CA=25 (or10)mm, Max. Retardation=400nm,

Resolution=0.5nm

Space needed(Lxwxh)≈110x229.4x165.4mm 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 )

UV Laser Beam Dump

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

~8mm Gaussian Beam Exit Window

Intra-cavity Shutter

~1.5m The Beam Expander (355nm):

Galilean, 2-8x magnification.

Focusing on sliding rails.

The Laser (Tripled Nd:Yag, 355nm):

M²<1.2 => spot roundness better than 85%.

Waist (single mode radius) = 0.13mm (420mm behind laser output).

Waist (mixed modes radius) = 0.1424mm.

Divergence 1.8mRad.

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

The Beam-Transfer

LLT

IR

m4

m3

Laser Box

SOAR Elevation Ring

m4: slow active x, y. Centers the beam on m3.

LLTm1: slow (~1Hz) active x, y. Pointing correction loop.

Laser box: x, y as a whole.

Centers the beam on m4.

m3: one-time x, y adjustments. Aligns LLT optical axis to Beam Transfer.

September 28, 2007 LGS for SAM – PDR – Optics 11

Polarization Issues

~/4

Goal:

>90% LGS return flux reaches the S-H CCD. UV

VIS

S-B

B-E

Laser Linear pol. horizontal

8mm GB circularly polarized

WFS Field Stop

/4

Retarder

SAM LGS WFS

The Goal:

>90% LGS

return flux

reaches the

S-H CCD.

September 28, 2007 LGS for SAM – PDR – Optics 12

The Polarization Strategy

polarization

-1

-0.5

0

0.5

1

-1 -0.5 0 0.5 1

phase=p

phase=2p-p/10

p=/2The Laser pol. is Linear Horizontal.

The S-B is ~4 (adjusted in lab).

The S-B is adjusted so that the back-scatter from LGS collected by the SOAR telescope is Circularly Polarized at Nasmyth.

The SAM common path and the WFS Optics may introduce some s-p de-phase.

This phase retardation is constant and will be measured. If the de-phase error ≥ /14 flux loss ≥ ~10%), it can be compensated in the WFS path.

September 28, 2007 LGS for SAM – PDR – Optics 13

The Optical Tolerances

LGS System Tolerances    

  Surface Shape Tolerance Decenter Dec. Tilt Tilt

Component Conic Radius Tolerance r Resol. Tolerance Resol.

    (mm) (mm) (um) (Deg) (Arcsec)

B-E --- --- 0.057 --- 0.0032 ---

Laser Box --- --- (0.1) 0.304 --- 0.0027 ---

m4 --- --- (0.1) 19.958 --- 0.0032 ---

m3 --- --- (0.1) 6.845 --- 0.0360 3.5

LLTm2 0.0390 0.1 0.073 --- (0.06) 0.1407 ---

LLTm1 0.0012 0.1 0.073 < 0.5 0.0045 (< 0.2)

LLT --- --- (0.1) 0.301 --- 0.0086 ---

LLTm1-LLTm2 distance: Z range=36um (7km to ∞); Z resolution=2.5um (depth of focus ~1000m).

Note1: The tolerance on Radius is driven by the mechanism’s designed focusing range ~0.5mm.Note2: 0.1mm is the ”standard” position accuracy and 1mrad the angular, to be expected in fabrication.

Table 6. Summary of tolerancing considerations for the LGS optical components.

Merit function:

GB waist 1/e² diam.=8mm on LLTm2.

GB waist at 10km from SOAR M1.

Image Strehl =0.8.

Image off-axis = 30”.

September 28, 2007 LGS for SAM – PDR – Optics 14

The Opto-mechanical Specs

Table 11. The complete LGS components positional, angular and adjustment specs for mechanical engineering.______________________________________________________________________________________Component Pos.Tol.(mm) Pos.Range (mm) Pos.Res(mm) Angular Tol.(º) Tilt Range(º) Tilt Res.(º)

______________________________________________________________________________________Laser Head 0.1 N/A N/A N/A N/A N/A Dump-Switch Mirror 0.1 N/A N/A 0.06 In-Out (~30º) (Repeat.~0.06º)Blue Laser 0.1 N/A N/A 0.06 N/A N/A Am1 0.1 N/A N/A 0.06 ±2 N/A Am2 0.1 In-Out (30mm) (Repeat.~10um) 0.06 ±2 N/A B-E 0.057 ±2 0.050 0.06 ±1 0.0032 S-B comp. 0.1 N/A N/A N/A N/A N/A Window 0.1 N/A N/A 0.06 N/A N/A Laser-Box (as a unit) 0.1 N/A N/A 0.06 ±0.5 0.0027 m4 0.1 N/A N/A 0.06 ±2 0.0032 m3 0.1 N/A N/A 0.06 ±2 0.0035 LLTm2 0.073 (Z±0.2,washer/spacers) (Z=0.1washers) 0.06 N/A N/A LLTm1 0.073 ±0.5 0.0005 0.0045 ±0.057 0.00005 LLT (as a unit) N/A N/A N/A 0.0086 ±0.167 0.0014 LLTm1-LLTm2 (z-axis) 0.1 ±0.1 0.0025 N/A N/A N/A _____________________________________________________________________________________

September 28, 2007 LGS for SAM – PDR – Optics 15

The Coatings for LGS Optics

Component Component Coating Component/Coating Code Plot

  Manufacturer Provider    #

Dump-switch mirror CVI CVI Y3-1025-45-UNP 1

Am1 CVI CVI BBDS-PM-1037-C 2

Am2 CVI CVI BBD1-PM-1037-C 3

Beam expander (8 surf.) Special Optics Special Optics AR-355 (T>97%) 4

S-B compensator (4 surf.) Special Optics Special Optics AR-355 (T>97%) 4

Laser box window (2 surf.) CVI CVI W2-PW1-1025-UV-355-0 4

m4 CVI CVI BBDS-PM-2037-C 2

m3 CVI CVI Y3-1025-45-UNP 1

LLTm2 CVI CVI Y3 on Al 5

LLTm1 Axsys Tech. CVI ? Y3 on Al 5

September 28, 2007 LGS for SAM – PDR – Optics 16

The Coatings for LGS Optics

Plot2 (BBDS) Plot1 (Y3)

Plot3 (BBD1) CVI_AR_355nm

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

250 300 350 400 450

Wavelength, nm

%R

Plot4

September 28, 2007 LGS for SAM – PDR – Optics 17

The Coatings for LGS Optics

Plot5

September 28, 2007 LGS for SAM – PDR – Optics 18

Damage Thresholds for LGS Optical Surfaces

Opt. laserGB Laser GB Laser GB Dmg.Thrs. Dmg.Thrs CW Pulsed Dust Factor Dusty Optics

  Diam. Pulsed CW CW Pulsed Safety Safety (absorp. fraction) Safety Factor

El. (mm) (MW/cm2) (kW/cm2) (kW/cm2) (MW/cm2) Factor Factor Min Max Min Max

Mirr 1 3.74 1.27 2 15 2 4 0.007 0.025 0.3 1

  4 0.23 0.08 2 15 25 64 0.007 0.025 4 11

  8 0.06 0.02 2 15 101 256 0.007 0.025 17 42

lens 1 3.74  N/A N/A 300 N/A 80 0.007 0.025 13 33

  2 0.94   " " 300 " 320 0.007 0.025 54 134

  4 0.23 " " 300 " 1282 0.007 0.025 215 536

  8 0.06   " " 300 " 5127 0.007 0.025 858 2143

If Absorption fraction of the optical element is a: (Where a= (1-R) for mirrors and (1-T) for lenses).

And df: is the T(orR) loss due to absorption by dust.

Safety Factor: (sfclean)= a(Dam.Thres.power)/a(GBpower)

Safety Factor: (sfdusty)= Damage Threshold/((1-df)(GB)+df/a(GB))

Conclusion: Only element with some risk (in ~6month period) is the laser beam-dump switching mirror.

September 28, 2007 LGS for SAM – PDR – Optics 19

Issues for Discussion and To Do List

Discussion:

LLTm1 tip-Tilt actuators.

LLTm2 focusing.

LLTm1 to m2 spacing control ?

To Do:

LLTm2: last search for a paraboloidal mirror.

Do the Optics Procurement.

Do the Lab experiments for laser beam and polarization

control.