SAM PDR1 S OAR Adaptive Module LGS LGSsystem Andrei Tokovinin SAM LGS Preliminary Design Review September 2007, La Serena

SAM PDR2 SAM at a glance (slide from 2003)

SAM PDR3 Why do we need SAM? FWHMEE(0.3”) SOAR0.56”0.127 SAM0.28”0.218 Typical conditions, 0.7  m, z=0 o SOAR is (must be) a high-resolution telescope! SAM PSF without SAM Seeing histograms

SAM PDR4 Rayleigh LGS timing Range gate defines the spot elongation and flux

SAM PDR5 Rayleigh laser at MMT 25W at 532nm

SAM PDR6 SAM design strategy Use standard commercial components whenever possible, not custom items Get a robust system – “set and forget” Provide margin in performance

SAM PDR7 Why this PDR? The SAM team has designed the LGS system, but… we have no prior experience and need advice. Current LGS design is PRELIMINARY, can be improved with panel’s input! SAM LGS Trade studies Laser choice Fast shutter Optical design Alignment Mechanical design Safety Requirements

SAM PDR8 Why a UV laser? UV not visible – no visual hazards More scattered photons (~ - 3 ) Easy to separate from the science Smaller launch telescope Cheap industrial lasers available: Nd:YAG frequency- tripled, =355nm (material processing) Less W per $ compared to 532nm Less efficient optics & detector, absorption in air Why not?

SAM PDR9 LGS trade studies Return flux calculation Fast shutter with Pockels cell (test) Select altitude and range gate Select the laser LLT and beam transfer concept Interfaces with SOAR

SAM PDR10 Return flux Laser power 10W at 355nm Loop time 4.3ms Spot elongation 1” Includes SAM efficiency (0.086), air absorption and density We need >300 photons! We have them, on paper flux absorption

SAM PDR11 Fast shutter – Pockels cell QX1020 cell Cleveland Crystals HV driver from BME

SAM PDR12 Ringing of the Pockels cell Centroids of inner spots are displaced by 9-90 mas depending on the seeing After-pulse contains 20% of light H=7km 1” seeing 1” elongation

SAM PDR13 Altitude and range gate Begin with H=7km and elongation 1” to maximize the flux. Change later if required

SAM PDR14 Select the laser: JDSU Cost, lower power, robustness, umbilical length MMT experience (no trouble in 4 years) Laser modelDS20-355Q301-HD Power, W at 10kHz810 Beam quality M 2 <1.1<1.2 Cost, k$ Plug power, kW< typ. Umbilical cable, m37

SAM PDR15 Laser at JDSU August 31, 2007 Q301-HD is used in the microprocessor industry 24/7. Several hundred are made

SAM PDR16 Laser Launch Telescope Aperture diameter 30cm 30cm  50cm * ( 355 / 589 ) Located behind SOAR M2 Mass <8kg (!?), length <0.7m Diffraction-limited at 355nm Ground-layer seeing 1” LLT design with a light-weight aluminum mirror (A. Montane)

SAM PDR17 Beam transport  Small beam inside tube  Flexure not critical  Active pointing in LLT Laser and its power supply/chiller need thermal cabinets Return polarization: Rayleigh scattering – yes Aerosol scattering - no

SAM PDR18 Laser electronics & chiller Electronics: 427x363x76mm, 8.4kg, 400W typ. Chiller: 533x440x264mm, 55kg, 700W typ., horizontal

SAM PDR19 Beam transport & control Power and LLT illumination Pointing on the sky Beam quality and focus BEAM CONTROL

SAM PDR20 SOAR flexure tests M2 displacement 2.2mm, tilt 77” zenith-to-horizon, mostly due to the elevation ring’s sag (confirmed by the FEA analysis of D.Neill) LLT mass 13kg has no effect on M2 (<20  m and <0.7”) Active control of M4 may be necessary Laser box on the truss OK (FEA calculation)

SAM PDR21 SOAR-LLT relative flexure Relative angle between the SOAR optical axis (source at the Nasmyth rotator center, active optics ON) and the LLT is less than +- 5”

SAM PDR22 Interfaces of LGS with SOAR Laser box on the SOAR truss Laser cable goes through regular cable wrap Laser electronics & chiller in a thermal cabinet LLT mounted behind M2 at 3 points Beam duct and relay mirror M4 Safety system Observatory interlock system

SAM PDR23 THE END

SAM PDR24 Electrical connections

SAM PDR25 SAM in numbers DMBimorph, 50mm pupil, 60 electrodes WFSS-H 10x10, CCD-39 pixel 0.37” LaserTripled Nd:YAG 355nm, 10W, 10 kHz LLTD=30cm, behind secondary, H=7km GatingKD*P Pockels cell, dH=120m Tip-tiltTwo probes, fiber-linked APDs, R<18 Focal plane 3’x3’ square, 3 arcsec/mm, f/16.5 CCD imager 4Kx4K, 0.05” pixels, 6 filters Coll. space50mm beam, 100mm along axis

SAM PDR26 Tip-tilt guiders: the field 4’x4’ surface