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LGS for SAM Optical Design

LGS for SAM Design Review September 2007, La Serena. LGS for SAM Optical Design. R.Tighe, A.Tokovinin. Laser Box on one of the serrurier trusses at bent-cass port #2 at 45Deg from IR Nasmyth. Working solution:

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LGS for SAM Optical Design

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

  2. LGS for SAM – PDR – Optics Laser Box on one of the serrurier trusses at bent-cass port #2 at 45Deg from IR Nasmyth. Working solution: Laser control and cooler position (on the ledge at the IR Nasmyth pillow-block level). IR Nasmyth Optical Nasmyth Beam Transfer Laser Launch Telescope 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). The LGS System on SOAR

  3. LGS for SAM – PDR – Optics Laser cable layout fit-test (yellow line). The Laser control & Cooler Rack. Cable length = 7m. The Laser umbilical cable handling on SOAR

  4. LGS for SAM – PDR – Optics Cable-wrap; mobile truss Cable-wrap;static Yellow line is the 7m Laser Umbilical Cable Layout IR Nasmyth Focus Rack for laser control, power and Cooler at pillow-block level Laser Cable and Rack at IR-Nasmyth

  5. LGS for SAM – PDR – Optics Requirements: • LLTm1: R=1000mm, F=300mm (pupil). • GB 1/e² diameter footprint on LLTm1=260mm. LLT m3 m4 Decided: • LLTm2: R=30mm, F=15mm. Laser Box SOAR Elevation Ring IR The LGS system (GB propagation)

  6. LGS for SAM – PDR – Optics 8mm Gaussian Beam Exit Window Soleil-Babinet Compensator 8x Beam Expander Beam ProfilerCCD Alignment Mirrors Am1&Am2 (coating450-700nm ) 355nm laser-line Dump switch-Mirror UV Laser Beam Dump Intra-cavity Shutter Blue Alignment Laser( 473nm) (or better400-420nm?) 355nm Tripled Nd:Yag Laser VIS UV LLT Laser Launch Telescope Laser-Box Beam Transfer The LGS system

  7. LGS for SAM – PDR – Optics • The optimized LLT: LLTm1: Diameter(mm) Radius(mm) Conic 300 1000 -0.99979 LLTm2: Diameter(mm) Radius(mm) Conic 15 15 -1.00001 13 to 24mm1/e² diameter GB Image at 7 to 14km from SOAR M1, respectively. 30Arcsec Field (on sky) LLT The Laser Launch Telescope 485mm

  8. LGS for SAM – PDR – Optics • 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 Comatic PSF 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 30Arcsec Field (on sky) LLT The Laser Launch Telescope 485mm

  9. LGS for SAM – PDR – Optics ~8mm Gaussian Beam Exit Window Soleil-Babinet Compensator 8x Beam Expander Beam ProfilerCCD Alignment Mirrors Am1&Am2 (coating450-700nm ) 355nm laser-line Dump switch-Mirror UV Laser Beam Dump ~1.5m Intra-cavity Shutter Blue Alignment Laser (473nm) (or better400-420nm?) VIS 355nm Tripled Nd:Yag Laser UV The Laser-Box • 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. • The Beam Expander (355nm): Galilean, 2-8x magnification. Focusing on sliding rails. • 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

  10. LGS for SAM – PDR – Optics LLT • LLTm1: slow (~1Hz) active Qx, Qy. Pointing correction loop. m3 • m3: one-time Qx, Qy adjustments. Aligns LLT optical axis to Beam Transfer. m4 • m4: slow active Qx, Qy. Centers the beam on m3. • Laser box: Qx, Qy as a whole. Centers the beam on m4. Laser Box SOAR Elevation Ring IR The Beam-Transfer

  11. LGS for SAM – PDR – Optics 8mm GB circularly polarized SAM LGS WFS S-B B-E WFS Field Stop l/4 Retarder The Goal: • >90% LGS return flux reaches the S-H CCD. VIS UV Laser Linear pol. horizontal Polarization Issues ~l/4 Goal: >90% LGS return flux reaches the S-H CCD.

  12. LGS for SAM – PDR – Optics p=p/2 The Polarization Strategy • The Laser pol. is Linear Horizontal. • The S-B is ~l/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 ≥ l/14 flux loss ≥ ~10%), it can be compensated in the WFS path.

  13. 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”. Table 6. Summary of tolerancing considerations for the LGS optical components. The Optical Tolerances 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 _____________________________________________________________________________________ LGS for SAM – PDR – Optics

  15. The Coatings for LGS Optics LGS for SAM – PDR – Optics

  16. Plot1 (Y3) Plot2 (BBDS) Plot4 Plot3 (BBD1) The Coatings for LGS Optics LGS for SAM – PDR – Optics

  17. Plot5 The Coatings for LGS Optics LGS for SAM – PDR – Optics

  18. LGS for SAM – PDR – Optics Damage Thresholds for LGS Optical Surfaces 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.

  19. LGS for SAM – PDR – Optics 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.

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