MCAO Laser Launch Telescope and Periscope Celine d’Orgeville and Jim Catone

MCAO May 24-25, 2001MCAO Preliminary Design Review2 On-axis, behind secondary mirror Do not obstruct secondary mirror central hole when MCAO not in use  CoDR: deployable primary mirrorLLT  PDR: PERISCOPE

MCAO May 24-25, 2001MCAO Preliminary Design Review3 LLT requirements ParameterSpecification Magnification ratio60 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 > nm ~ 50 % in the visible ( nm) Optics and coatings Can sustain power densities in the W/cm 2 range

MCAO May 24-25, 2001MCAO Preliminary Design Review4 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 High order aberrations Decrease in SNR < 10% (5%) High order ab. <0.06 wave rms

MCAO May 24-25, 2001MCAO Preliminary Design Review5 LLT image quality specs for MCAO Wavefront aberrations RequirementGoal Tip/Tilt ( dynamic) < 0.1 Hz Hz 1-30 Hz > 30 Hz (in arcsec on the sky) < 10’’ peak < 1’’ peak < 0.2’’ peak < 0.03’’ rms 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

MCAO May 24-25, 2001MCAO Preliminary Design Review6 LLT optical design 16mm toroidal fold mirror 10mm silica aspheric lens 450mm, f=1672.3mm, 258mm off- axis parabola

MCAO May 24-25, 2001MCAO Preliminary Design Review7 Optical perf. over ±1 arcmin FoV for a uniformly illuminated 450mm STOP

MCAO May 24-25, 2001MCAO Preliminary Design Review8 Optical perf. over ±1 arcmin FoV for a uniformly illuminated 300mm STOP

MCAO May 24-25, 2001MCAO Preliminary Design Review9 Encircled energy over ±1.2 arcmin FoV

MCAO May 24-25, 2001MCAO Preliminary Design Review10 Gemini Telescope’s Top End Assembly Mounting Surface For the LLT Electronics Boxes f/16 Top End Secondary Mirror Module Secondary Support Structure (SSS) Top End Vanes Vane Ring SSS/M2 Interface Plane

MCAO May 24-25, 2001MCAO Preliminary Design Review11 Gemini Telescope’s Secondary Support Structure 3D View of the SSS Reference Plane ± Figures taken from drawings ICR01 and ICR02

MCAO May 24-25, 2001MCAO Preliminary Design Review12 SSS/LLT/BTOOB Alignment 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 Secondary Support Structure Laser Launch Telescope Beam Transfer Optics Optical Bench

MCAO May 24-25, 2001MCAO Preliminary Design Review13 4X LLT/SSS Interface Pad LLT Top Plate Interfaces 3X LLT/BTOOB Interface Pad F F X LLT/SSS Location Pin Access Port +X-X +Y -Y 2X LLT/BTOOB Alignment Pin Location PLAN VIEW

MCAO May 24-25, 2001MCAO Preliminary Design Review14 LLT Interface Details LLT/SSS AlignmentLLT/BTOOB Alignment SSS Top Plate M20 Nut & Washer ½” Locating Pin 1.0 mm Raised Pad 5.0 mm Thick Shim BTO Optical Bench LLT Top Plate w/ M20 Stud LLT Pilot Hole Access Port 1.0 mm Raised Pads ¼” Locating Pin M12 Bolt & Washer M12 Threaded Insert

MCAO May 24-25, 2001MCAO Preliminary Design Review15 Passive Focus Compensation Configuration Off-Axis Distance DETAIL 1 1 Fold Mirror Diverging Lens Incoming Beam Translation Table Compensation Rod Theoretical Mirror Mounting Plane Exiting Beam Produces a maximum error of 2.5 nm in the temperature range of 0 ± 15°

MCAO May 24-25, 2001MCAO Preliminary Design Review16 Passive Compensation Analysis r = b = Compensation Rod Length b c B A a C CONSTANTS b = mm B = 81.2° c = mm

MCAO May 24-25, 2001MCAO Preliminary Design Review17Periscope 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

MCAO May 24-25, 2001MCAO Preliminary Design Review18 Periscope Optical Design 180mm Hole in M2 (Actual Hole is 168 mm) Focus Target at Height of BTOOB/LLT Assembly PM2 Parent Mirror PM1 Parent Mirror 8M Telescope Axis  = 10°±1° 3.5° to 4.5° Exclusion Angle on the Sky

MCAO May 24-25, 2001MCAO Preliminary Design Review19 Secondary Mirror Bracket Mirror Cover Assembly Primary Mirror Bracket Primary Mirror Secondary Mirror Periscope Subsystem

MCAO May 24-25, 2001MCAO Preliminary Design Review20 Periscope Location (SSS) SSS Cross Bracing Periscope Assembly SSS Top End Vane Interface

MCAO May 24-25, 2001MCAO Preliminary Design Review21 Periscope Clearance Within the SSS SSS Cross Bracing Periscope Assembly Secondary Mirror Bracket SSS Vertical Beams

MCAO May 24-25, 2001MCAO Preliminary Design Review22 Periscope Location (M2) f/16 Secondary Mirror (M2) M2 Positioning Mechanism M2 Tilt Mechanism Beam Path Periscope Assembly LLT 168 mm Optical Stop SSS M2 Mounting Plate

MCAO May 24-25, 2001MCAO Preliminary Design Review23 Periscope Orientation +X-X +Y -Y SSS Surface w/ Vertical I-Beams Existing M2 Hole Cover Assembly Outline Periscope Assembly F F Primary/Secondary Bracket Interface

MCAO May 24-25, 2001MCAO Preliminary Design Review24 Periscope Mirror Mounting 115° Offset Spherical Mount Secondary Bracket Flange Primary Mirror Primary Mirror Bracket Axis of Symmetry

MCAO May 24-25, 2001MCAO Preliminary Design Review25 Periscope Mirror Mounting Details Mirror Mount w/ M6 Stud M6 Nut and Large OD Washer Spherical Seat Primary Mirror Surface Spherical Washer

MCAO May 24-25, 2001MCAO Preliminary Design Review26 Periscope Mirror Cover Secondary Mirror Mirror Cover Motor Bracket Mirror Cover Motor Aluminum Hinge Mirror Cover 2-Bar Linkage Secondary Mirror Bracket

MCAO May 24-25, 2001MCAO Preliminary Design Review27 Periscope Mirror Cover Open & Closed Positions Outgoing Beam Mirror Cover Motor Bracket 2-Bar Linkage Mirror Cover (Open) Secondary Mirror Bracket Secondary Mirror Incoming Beam 98.3° Limit Switches

MCAO May 24-25, 2001MCAO Preliminary Design Review28 Mass Allocation Total Mass Added to the SSS 125 ±25 kg BTOOB Mass 20 kg LLT Mass 120 kg Periscope Mass 10 kg

MCAO May 24-25, 2001MCAO Preliminary Design Review29 PDR Agenda PDR Agenda Thursday, 5/ Welcome 0805 Project overview 0830 Science case 0930 Break 0945 System overview 1015 System modeling 1100 AO Module optics 1145 Lunch 1245 AO Module mechanics 1340 AO Module electronics 1400 Break 1415 Beam Transfer Optics 1510 Laser Launch Telescope 1545 Closed committee session 1800 Adjourn