SAM PDR 1

SSOAROAR

AAdaptivedaptiveMModuleodule LGSLGSsystemsystem

Andrei Tokovinin

SAM LGS Preliminary Design Review September 2007, La Serena

SAM PDR 2

SAM at a

glance

(slidefrom2003)

SAM PDR 3

Why do we need SAM?

FWHM EE(0.3”)

SOAR 0.56” 0.127

SAM 0.28” 0.218

Typical conditions, 0.7 m, z=0o

SOAR is (must be) a high-resolution

telescope!SAM PSF

without SAM

Seeing histograms

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Rayleigh LGS timing

Range gate definesthe spot elongationand flux

SAM PDR 5

Rayleigh laser at MMT

25W at 532nm

SAM PDR 6

SAM design strategy

Use standard commercial components whenever possible, not custom items

Get a robust system – “set and forget”

Provide margin in performance

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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 shutterOptical design

Alignment

Mechanical design Safety

Requirements

SAM PDR 8

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 PDR 9

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

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Return flux

Laser power 10W at 355nmLoop time 4.3msSpot elongation 1”

Includes SAM efficiency (0.086), air absorption and density

We need >300 photons!We have them, on paperflux

absorption

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Fast shutter – Pockels cell

QX1020 cell

Cleveland Crystals

HV driver from BME

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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=7km1” seeing1” elongation

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Altitude and range gate

Begin with H=7km and elongation 1” to maximize the flux.Change later if required

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Select the laser: JDSU

Cost, lower power, robustness, umbilical length

MMT experience (no trouble in 4 years)

Laser model DS20-355 Q301-HD

Power, W at 10kHz 8 10

Beam quality M2 <1.1 <1.2

Cost, k$ 115 110

Plug power, kW <2.2 1.1 typ.

Umbilical cable, m 3 7

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Laser at JDSU

August 31, 2007

Q301-HD is used in the microprocessor industry 24/7.

Several hundred are made

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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-weightaluminum mirror (A. Montane)

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Beam transport

Small beam inside tubeFlexure not criticalActive pointing in LLT

Laser and its power supply/chiller needthermal cabinets

Return polarization:Rayleigh scattering – yesAerosol scattering - no

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Laser electronics & chiller

Electronics: 427x363x76mm, 8.4kg, 400W typ.

Chiller: 533x440x264mm, 55kg, 700W typ., horizontal

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Beam transport & control

Power and LLT illumination

Pointing on the sky

Beam quality and focus

BEAM CONTROL

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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 (<20m and <0.7”)

Active control of M4 may be necessary

Laser box on the truss OK (FEA calculation)

SAM PDR 21

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”

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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

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THE END

SAM PDR 24

Electrical connections

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SAM in numbers

DM Bimorph, 50mm pupil, 60 electrodes

WFS S-H 10x10, CCD-39 pixel 0.37”

Laser Tripled Nd:YAG 355nm, 10W, 10 kHz

LLT D=30cm, behind secondary, H=7km

Gating KD*P Pockels cell, dH=120m

Tip-tilt Two 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. space 50mm beam, 100mm along axis

SAM PDR 26

Tip-tilt guiders: the field

4’x4’ surface