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MCAO Laser Launch Telescope and Periscope Celine d’Orgeville and Jim Catone MCAO LLT • On-axis, behind secondary mirror • Do not obstruct secondary mirror central hole when MCAO not in use CoDR: deployable primary mirror PDR: PERISCOPE May 24-25, 2001 MCAO Preliminary Design Review 2 LLT requirements MCAO Parameter Specification Magnification ratio 60 with a 1% tolerance Field of View +/- 1.2 arcmin (unvignetted) +/- 1.0 arcmin (for image quality spec.) Optical design No central obscuration No internal focus ~ 450mm STOP Focus adjustment Fixed afocal telescope (passive comp. preferred) Optical transmission > 97 % @ 589nm ~ 50 % in the visible (450-700nm) Optics and coatings Can sustain power densities in the 5001000 W/cm2 range May 24-25, 2001 MCAO Preliminary Design Review 3 MCAO LLT image quality analysis for MCAO • LGS WFS centroiding measurement error must not increase by more than 20% (req.)/ 10% (goal) Low order aberrations • LGS spot size increase < 10% (5%) • • • • • Defocus <0.1 wave rms Astig <0.18 wave rms Coma <0.1 wave rms Trefoil <0.25 wave rms Spherical <0.1 wave rms May 24-25, 2001 High order aberrations • Decrease in SNR < 10% (5%) • High order ab. <0.06 wave rms MCAO Preliminary Design Review 4 LLT image quality specs for MCAO Wavefront aberrations Requirement Tip/Tilt ( dynamic) < 0.1 Hz 0.1-1 Hz 1-30 Hz > 30 Hz (in arcsec on the sky) < 10’’ peak < 1’’ peak < 0.2’’ peak < 0.03’’ rms MCAO Goal Low order aberrations < 0.15 wave rms < 0.1 wave rms High order aberrations < 0.06 wave rms < 0.04 wave rms All other performance being equal, this would save a 15% increase in laser power requirement May 24-25, 2001 MCAO Preliminary Design Review 5 MCAO LLT optical design 16mm toroidal fold mirror 10mm silica aspheric lens May 24-25, 2001 450mm, f=1672.3mm, 258mm offaxis parabola MCAO Preliminary Design Review 6 Optical perf. over ±1 arcmin FoV for a uniformly illuminated 450mm STOP May 24-25, 2001 MCAO Preliminary Design Review MCAO 7 Optical perf. over ±1 arcmin FoV for a uniformly illuminated 300mm STOP May 24-25, 2001 MCAO Preliminary Design Review MCAO 8 MCAO Encircled energy over ±1.2 arcmin FoV May 24-25, 2001 MCAO Preliminary Design Review 9 Gemini Telescope’s Top End Assembly Secondary Support Structure (SSS) Top End Vanes Mounting Surface For the LLT Electronics Boxes Vane Ring f/16 Top End SSS/M2 Interface Plane May 24-25, 2001 MCAO Secondary Mirror Module MCAO Preliminary Design Review 10 Gemini Telescope’s Secondary Support Structure MCAO 25.0 2348.0 2178.0 2323.0 2148.0 2153.0 1084.0 ±7.0 475.0 Reference Plane 3D View of the SSS • Figures taken from drawings ICR01 and ICR02 May 24-25, 2001 MCAO Preliminary Design Review 11 SSS/LLT/BTOOB Alignment Secondary Support Structure • • • • • • Laser Launch Telescope MCAO Beam Transfer Optics Optical Bench First align the BTOOB to the LLT and pin Remove the BTOOB and loosely install the LLT in the SSS Reinstall the BTOOB on the LLT Align the BTOOB/LLT assembly with the SSS Remove the BTOOB and pin the LLT/SSS interface Finally, reinstall the BTOOB May 24-25, 2001 MCAO Preliminary Design Review 12 LLT Top Plate Interfaces PLAN VIEW +Y MCAO 3X LLT/BTOOB Interface Pad 4X LLT/SSS Interface Pad F910.0 -X +X F500.0 2X LLT/BTOOB Alignment Pin Location May 24-25, 2001 -Y MCAO Preliminary Design Review 2X LLT/SSS Location Pin Access Port 13 MCAO LLT Interface Details LLT Top Plate w/ M20 Stud BTO Optical Bench M12 Bolt & Washer LLT Pilot Hole Access Port 1.0 mm Raised Pads ¼” Locating Pin 15.0 24.0 25.0 SSS Top Plate ½” Locating Pin M20 Nut & Washer 1.0 mm Raised Pad 5.0 mm Thick Shim LLT/SSS Alignment May 24-25, 2001 M12 Threaded Insert LLT/BTOOB Alignment MCAO Preliminary Design Review 14 Passive Focus Compensation Configuration MCAO 258.0 Off-Axis Distance 1 Exiting Beam 1631.5 1682.3 Incoming Beam Translation Table Fold Mirror Diverging Lens Compensation Rod Theoretical Mirror Mounting Plane DETAIL 1 • Produces a maximum error of 2.5 nm in the temperature range of 0 ± 15° May 24-25, 2001 MCAO Preliminary Design Review 15 MCAO Periscope • Why ? – 168mm M2 hole to avoid narcissus effect when observing in thermal IR – M2 hole blocked by LLT, IR instrument can no longer see sky • How ? – Two-mirror periscope to divert the beam around the SSS – Mirror cover to block beam during visible observations – Oversized FoV and STOP to allow for M2 tip/tilt and decentrations and telescope flexures • Where ? – Bottom of SSS – Replace Gemini central baffle • Who ? – Gemini designs, integrates and commissions – RFP for parts for GN and GS periscopes May 24-25, 2001 MCAO Preliminary Design Review 17 Periscope Optical Design 8M Telescope Axis a = 10°±1° 3.5° to 4.5° Exclusion Angle on the Sky MCAO Focus Target at Height of BTOOB/LLT Assembly PM1 Parent Mirror PM2 Parent Mirror May 24-25, 2001 180mm Hole in M2 (Actual Hole is 168 mm) MCAO Preliminary Design Review 18 Periscope Subsystem MCAO Primary Mirror Mirror Cover Assembly Primary Mirror Bracket Secondary Mirror Secondary Mirror Bracket May 24-25, 2001 MCAO Preliminary Design Review 19 Periscope Location (SSS) MCAO SSS Periscope Assembly Top End Vane Interface May 24-25, 2001 MCAO Preliminary Design Review SSS Cross Bracing 20 Periscope Location (M2) MCAO SSS LLT Periscope Assembly 475.0 35.0 M2 Mounting Plate M2 Positioning Mechanism 897.0 168 mm Optical Stop May 24-25, 2001 M2 Tilt Mechanism Beam Path MCAO Preliminary Design Review f/16 Secondary Mirror (M2) 22 Periscope Mirror Mounting Secondary Bracket Flange MCAO Axis of Symmetry Spherical Mount Primary Mirror Primary Mirror Bracket 115° Offset May 24-25, 2001 MCAO Preliminary Design Review 24 Periscope Mirror Cover Mirror Cover Motor MCAO Mirror Cover Motor Bracket Mirror Cover 2-Bar Linkage Aluminum Hinge Secondary Mirror May 24-25, 2001 Secondary Mirror Bracket MCAO Preliminary Design Review 26 Mass Allocation MCAO Total Mass Added to the SSS 125 ±25 kg LLT Mass 120 kg May 24-25, 2001 BTOOB Mass 20 kg MCAO Preliminary Design Review Periscope Mass 10 kg 28 MCAO PDR Agenda Thursday, 5/24 0800 Welcome 0805 Project overview 0830 Science case 0930 Break 0945 System overview 1015 System modeling 1100 AO Module optics 1145 Lunch May 24-25, 2001 1245 AO Module mechanics 1340 AO Module electronics 1400 Break 1415 Beam Transfer Optics 1510 Laser Launch Telescope 1545 Closed committee session 1800 Adjourn MCAO Preliminary Design Review 29