September 28, 2007LGS for SAM – PDR – Optics1 LGS for SAM Optical Design R.Tighe, A.Tokovinin. LGS for SAM Design Review September 2007, La Serena

September 28, 2007LGS for SAM – PDR – Optics2 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, 2007LGS for SAM – PDR – Optics3 The Laser umbilical cable handling on SOAR The Laser control & Cooler Rack. Cable length = 7m. Laser cable layout fit-test (yellow line).

September 28, 2007LGS for SAM – PDR – Optics4 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, 2007LGS for SAM – PDR – Optics5 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, 2007LGS for SAM – PDR – Optics6 Laser-Box 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 (coating nm ) UV Laser Beam Dump Blue Alignment Laser( 473nm) (or better nm?) 8mm Gaussian Beam Exit Window Intra-cavity Shutter LLT Laser Launch Telescope Beam Transfer The LGS system

September 28, 2007LGS for SAM – PDR – Optics7 The optimized LLT: LLT m 1: Diameter(mm) Radius(mm) Conic LLT m 2: Diameter(mm) Radius(mm) Conic mm 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, 2007LGS for SAM – PDR – Optics8 485mm LLT 30Arcsec Field (on sky) 13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively. OPDComa=57nm OPD rms = 59nm OPD p-v =115nm Strehl Ratio= 0.88 Comatic PSF The working LLT: LLT m 1 (pivots around center of curvature of LLT m 2): Diameter(mm) Radius(mm) Conic LLT m 2: Diameter(mm) Radius(mm) Conic The Laser Launch Telescope

September 28, 2007LGS for SAM – PDR – Optics9 The Laser-Box The S-B compensator (UV): 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 (coating nm ) UV Laser Beam Dump Blue Alignment Laser (473nm) (or better nm?) ~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 spot roundness better than 85%. Waist (single mode radius) = 0.13mm (420mm behind laser output). Waist (mixed modes radius) = mm. Divergence 1.8mRad.

September 28, 2007LGS for SAM – PDR – Optics10 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, 2007LGS for SAM – PDR – Optics11 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, 2007LGS for SAM – PDR – Optics12 The Polarization Strategy p=  /2 The 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, 2007LGS for SAM – PDR – Optics13 The Optical Tolerances LGS System Tolerances Surface Shape Tolerance DecenterDec. Tilt ComponentConicRadius Tolerance  r Resol. Tolerance  Resol. (mm) (um)(Deg)(Arcsec) B-E Laser Box--- (0.1) m4--- (0.1) m3--- (0.1) LLTm (0.06) LLTm < (< 0.2) LLT--- (0.1) 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, 2007LGS for SAM – PDR – Optics14 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 ± ± 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 ± m4 0.1 N/A N/A 0.06 ± m3 0.1 N/A N/A 0.06 ± LLTm (Z±0.2,washer/spacers) (Z=0.1washers) 0.06 N/A N/A LLTm ± ± LLT (as a unit) N/A N/A N/A ± LLTm1-LLTm2 (z-axis) 0.1 ± N/A N/A N/A _____________________________________________________________________________________

September 28, 2007LGS for SAM – PDR – Optics15 The Coatings for LGS Optics Component CoatingComponent/Coating CodePlot ManufacturerProvider # Dump-switch mirrorCVI Y UNP 1 Am1Am1CVI BBDS-PM-1037-C 2 Am2Am2CVI BBD1-PM-1037-C 3 Beam expander (8 surf.)Special Optics AR-355 (T>97%) 4 S-B compensator (4 surf.)Special Optics AR-355 (T>97%) 4 Laser box window (2 surf.)CVI W2-PW UV m4m4CVI BBDS-PM-2037-C 2 m3m3CVI Y UNP 1 LLTm2CVI Y3 on Al 5 LLTm1Axsys Tech.CVI ?Y3 on Al 5

September 28, 2007LGS for SAM – PDR – Optics16 The Coatings for LGS Optics Plot2 (BBDS) Plot1 (Y3) Plot3 (BBD1) Plot4

September 28, 2007LGS for SAM – PDR – Optics17 The Coatings for LGS Optics Plot5

September 28, 2007LGS for SAM – PDR – Optics18 Damage Thresholds for LGS Optical Surfaces Opt.laserGBLaser GB Dmg.Thrs.Dmg.ThrsCWPulsedDustFactorDustyOptics Diam.PulsedCW PulsedSafety (absorp.fraction)SafetyFactor El.(mm)(MW/cm2)(kW/cm2) (MW/cm2)Factor MinMaxMinMax Mirr lens13.74 N/A 300N/A ""300" ""300" ""300" 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: (sf clean )= a(Dam.Thres.power)/a(GBpower) Safety Factor: (sf dusty )= 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, 2007LGS for SAM – PDR – Optics19 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.