NGAO Alignment PlanSee KAON 719

P. Wizinowich

Introduction

• KAON 719 is intended to define & describe the alignments that will need to be performed to assemble the AO subsystems into the overall AO system and to align this system to the telescope.

• Subsystem alignments will be documented separately as deliverables for each subsystem.– A list of these subsystems/components is provided.

Starting Points• Defining Points & Axes

– Key axes (want to co-align all of these)• Telescope elevation axis (assuming telescope optical axis overlaps this).• AO rotator mechanical axis• Science instrument optical axis• Subsystem optical axes

– Key points• Telescope focal position • Telescope pupil position

• Models used for Alignment– Zemax model & tolerance analysis– SolidWorks model of AO bench, AO bench cold enclosure & AO room

enclosure– If appropriate export SolidWorks to coordinate measuring machine

(CMM) software (Probe arm or laser tracker approach)– These models need to be done at lab & operating temperatures

Requirements

System Requirement SR-55 defines the opto-mechanical alignment requirement to the telescope:– NGAO bench's optical axis shall be coincident with the telescope's

elevation axis to within the following requirements:• At the telescope's focal plane on the Nasmyth platform the separation of

these two axes shall be < 1 mm.• At the telescope's pupil the misalignment of the two axes shall be < 30 mm. 

– NGAO input focal plane should be made coincident with the telescope's nominal focal plane in focus to < 2 mm.

– The vector perpendicular to the NGAO bench surface should be parallel to gravity to < 2 arcmin.

– The above requirements should be met:• At all telescope elevations from zenith to 70 zenith angle.• Assuming a rotator, at all rotator angles. • At all dome environment operating temperatures.

Requirements Flowdown• Requirement of alignment of DAVINCI to AO bench optical axis evaluated

from several perspectives (x,y,z,x,y,z)– Overall will need the 3 instrument kinematic defining points to be adjustable at

~50 m level (unless cold pupil mask position is adjustable)

• Requirement for alignment of LGS WFS assembly– Overall need kinematic defining points adjustable at 0.25 mm level

• Calibration unit requirements to support alignments:– On-axis NGS source with a pupil stop matching the location and size of the

telescope pupil & with some adjustment in focus. Accuracy of the focus needs to be sufficient to optimize the image on the science instrument.

– On-axis sources, with a pupil stop matching the location & size of the telescope pupil, conjugate to at least 2 sodium layer altitudes, say 80 km & 150 km.

– The on-axis sources need to be positioned to <0.5" of the rotator axis.– The on-axis pupil stop needs to be centered on the rotator axis to <0.3% of the

pupil stop size.– Since the calibrator must be aligned this well with the AO bench at lab

temperature and also at the cold enclosure temperature the alignment must either not change with temperature or there must be a means of remotely realigning the beam to the above requirements (the latter is recommended).

AO System Alignment for Lab I&T• Install bench in clean room on vibration isolation legs.• Level bench versus gravity.• Mark out location of all components on bench based on SolidWorks model &

tolerances. • Install risers on bench for components that require risers.• If they do not interfere with future alignments components can be installed on the

bench as they are received & accepted.• Install & align the rotator (see section 3.2).• Install & align low order relay including fold mirror, two OAPs, sodium reflective

dichroic and LODM (or if necessary a flat mirror at the LODM location) (see section 3.3).

• Install & align the high order relay including fold mirror, two OAPs and HODM (or if necessary a flat mirror at the HODM location) (see section 3.3).

• Install & align acquisition camera (see section 3.4).• Install & align calibration unit & its fold mirror (see section 3.5). • Install & align NGS WFS assembly (see section 3.6).• Install & align LOWFS assembly (see section 3.7).• Install & align ADC (see section 3.9).• Align LGS WFS to AO bench (see section 3.8).• Align DAVINCI to AO bench (see section 3.10).Need to test system at lab & then at cold enclosure temperatures

AO System Alignment at Telescope

• Recommended approach is to transport fully assembled AO bench within its cold enclosure as a unit– Shipment procedure will require significant preparation & care

• Initial positioning on Nasmyth platform using SolidWorks model & within tolerances

• AO bench fiducial aligned to elevation axis– Fiducial (partially reflective mirror with cross-hair) installed on exterior

side of input window in lab & aligned to rotator axis

– Cross-hairs mounted on elevation axis

• LGS WFS, DAVINCI & Interferometer module subsequently aligned to AO bench– Could potentially also have fiducials for LGS WFS & DAVINCI

Open Issues

• Need to better quantify the alignment requirements to the AO bench for more of the subsystems – Have done this for DAVINCI & the LGS WFS

– Should do for LOWFS before PDR

– Others can probably wait until detailed design

• Alignment of LOWFS on AO bench requires more thought & discussion with LOWFS team

• Should determine if DAVINCI needs a pupil imaging mode– Have an alignment procedure without this but requires that DAVINCI

has a way to adequately align the pupil mask beforehand

• Should think through Gavel’s suggestion of using fold mirrors to correct for pupil misalignment