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S OAR A daptive M odule LGS system

SAM LGS Preliminary Design Review September 2007, La Serena. S OAR A daptive M odule LGS system. Andrei Tokovinin. SAM at a glance. (slide from 2003). Why do we need SAM?. SOAR is (must be) a high-resolution telescope!. SAM PSF. without SAM.

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S OAR A daptive M odule LGS system

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  1. SAM PDR SAM LGS Preliminary Design Review September 2007, La Serena SOAR Adaptive Module LGS system Andrei Tokovinin

  2. SAM PDR SAM at a glance (slide from 2003)

  3. Why do we need SAM? SOAR is (must be) a high-resolution telescope! SAM PSF without SAM Typical conditions, 0.7 m, z=0o Seeing histograms SAM PDR

  4. SAM PDR Rayleigh LGS timing Range gate defines the spot elongation and flux

  5. SAM PDR Rayleigh laser at MMT 25W at 532nm

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

  7. SAM PDR 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! Trade studies Laser choice Fast shutter Requirements Optical design SAM LGS Alignment Safety Mechanical design

  8. SAM PDR 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) Why not? • Less W per $ compared to 532nm • Less efficient optics & detector, absorption in air

  9. SAM PDR 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

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

  11. SAM PDR Fast shutter – Pockels cell QX1020 cell Cleveland Crystals HV driver from BME

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

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

  14. Select the laser: JDSU • Cost, lower power, robustness, umbilical length • MMT experience (no trouble in 4 years) SAM PDR

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

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

  17. SAM PDR 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

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

  19. SAM PDR Beam transport & control • Power and LLT illumination • Pointing on the sky • Beam quality and focus BEAM CONTROL

  20. SAM PDR 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)

  21. SAM PDR 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”

  22. SAM PDR 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

  23. SAM PDR THE END

  24. SAM PDR Electrical connections

  25. SAM PDR SAM in numbers

  26. SAM PDR Tip-tilt guiders: the field 4’x4’ surface

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