Katrin Dahl for the AEI 10 m Prototype team

AEI 10m Prototype

AEI 10 m Prototype and its

Suspension Platform Interferometer

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The team

» Harald Lück: Pretty much everything...» Kasem Mossavi: Vacuum system, infrastructure» Stefan Hild : Interferometer sensing and control

» Kentaro Somyia: Theory @ Caltech» Alessandro Bertolini: Isolation Tables

» Michael Born: CDS, Interface SPI2CDS » Fumiko Kawazoe: Frequency-Reference Cavity design and control» Gerrit Kühn : CDS and related infrastructure» Bob Taylor: Suspension Systems

» Katrin Dahl : Suspension Platform Interferometer» Christian Gräf : Digital Control» Tobias Westphal : Monolithic suspensions, IFO-control» Alexander Wanner : Seismic Isolation

» Oliver Kranz : Suspension Platform Interferometer» Daniel Gering : Interface SPI2CDS

» Andreas Weidner: Electronics

Ph.D Students

Diploma Student

Postdoctoral Research Fellow

Research Fellow

Staff scientist

Lecturer

Senior staff scientist

» Ken Strain: Scientific Leader of the 10m Prototype» StefanGoßler: Coordinator, Leader QUEST Research Group» Benno Willke : Leader QUEST task group, high power laser

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AEI 10 m PROTOTYPEAEI 10 m Prototype and its Suspension Platform Interferometer

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The AEI 10 m Prototype

Goals:

• Maximal overlap with GEO-HF subsystems– develop and prove as many of the techniques needed for GEO 600 upgrades

as possible (e.g. PSL, digital control infrastructure)– provide training for people who will install and run GEO-HF

• Provide ultra low displacement noise testing environment– To probe at (and later go beyond) the SQL– Entanglement of macroscopic test masses– For geodesy/LISA related experiments – ...

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IFO

Frequency reference cavity:- Finesse ~7500- roundtrip length 24.6 m- mirrors 850 g- Triple cascade all steel wire pendulum suspension

- monolithic all-silica last stage- silica suspension filaments of 28 µm diameter

- 100 g mirrors- triple cascaded pendulum suspensions

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The prototype hall

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Vacuum system

Tubes:1.5 m diameter

Volume ca. 100 m3 22 t stainless steel

Tanks:3 m diameter, 3.4 m tall

Tank centers separated by 11.65m

Roughing: One 170 l/s screw pump Main pumps: Two 2000 l/s turbo-molecular pumps Backing and differential pumping: Two scroll pumps

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270° view

• After 12 hours of pumping 10-6 mbar• After about one week of pumping 10-7 mbar

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GEO600 tank

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Walk-in tanks

100 mm flangesto fit feed throughs

600 mm flangesto fit viewports

100 mm flangesto fit feed throughs

Door into the tank

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Seismic Attenuation System

• One SAS per vacuum tank, optical table goes on top of SAS

• Improved version of HAM-SAS

• Resonance frequency around 0.1 Hz

• Up to 80 dB attenuationin both vertical and

horizontal directions

• Angstrom residual motion above 1 Hz

Relative residual motions between the tables will be detected and stabilised by the SPI

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Horizontal table actuation

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Vertical table actuation

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Vertical table actuation

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SPIAEI 10 m Prototype and its Suspension Platform Interferometer

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Why a Suspension Platform Interferometer?

• Ease lock acquisition of cavities by reducing residual test mass motion

• Reduction of burden to actuators on the mirrors

• Testbed for GRACE follow-on and LISA related experiments Sets requirements on SPI

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THE SPI

• Requirements:– No specific lock point– Control bandwidth 100 Hz– 100 pm/sqrt(Hz) and 10 nrad/sqrt(Hz) @ 10 mHz

• Heterodyne Mach-Zehnder interferometry– Suits our needs best– In-house knowledge

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Heterodyne Mach-Zehnder IFO

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Optical layout

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Measurement bench

• Beam height 45 mm• Overall height below 65 mm

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Phase determination

Phase is extracted from heterodyne signal by use of an hardware Phasemeter1 based on FPGA chips

1. Preamplifier and A/D conversion– Photocurrent converted to voltage– Digitising signals– results in time series

2. Single bin discrete Fourier transform – Fourier transform at only one frequency– complex amplitude of PD signal at fhet

3. Signal combination of each QPD quadrant leads to phase, DC, Differential Wavefront Sensing (DWS) and contrast information

Illustration of DWS

1 developed for LISA Pathfinder, Heinzel G et al. 2004 Class Quantum Grav 21 581

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Choice of parameters

• Due to the arm length mismatch (20 m optical path length) a highly stabilised laser is necessary:

• 140 Hz/sqrt(Hz) @ 10 mHz for IR light (1064 nm)

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Iodine stabilised Nd:YAG laser

Michael Tröbs

outputpower: 1 W

Stabilisation via Modulation Transfer Spectroscopy

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Choice of parameters

• According to the arm length mismatch (20 m optical path length) a highly stabilised laser is necessary:

• 140 Hz/sqrt(Hz) @ 10 mHz for IR light (1064 nm)

• Control bandwidth 100 Hz heterodyne frequency around 20 kHz new phasemeter interface needed

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Phasemeter InterfaceTransfer rate from phasemeter EPP to microcontroller ethernet around 1.9 kHz with 16 channels

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Choice of parameters

• According to the arm length mismatch (20 m optical path length) a highly stabilised laser is necessary:

• 140 Hz/sqrt(Hz) @ 10 mHz for IR light (1064 nm)

• Control bandwidth 100 Hz heterodyne frequency around 20

kHz

• Thermal drifts requires components to be monolithically bonded to plate with low CTE (ClearCeram, CTE=0.4*10-7/K)

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Optical layout

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Expected transversal signalsco

ntra

stDC

Phas

e di

ffere

nce

[rad

]DW

S [r

ad]

-2 -1 0 1 2Transveral displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Transveral displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Transveral displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Transveral displacement of MW1 or MS1 [mm]

Red curve: PDCW1Black curve: PDCS1

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Expected longitudinal signalsco

ntra

stDC

Phas

e di

ffere

nce

[rad

]DW

S [r

ad]

-2 -1 0 1 2Longitudinal displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Longitudinal displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Longitudinal displacement of MW1 or MS1 [mm]

-2 -1 0 1 2Longitudinal displacement of MW1 or MS1 [mm]

Red curve: PDCW1Black curve: PDCS1

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Expected rotational signalsco

ntra

stDC

Phas

e di

ffere

nce

[rad

]DW

S [r

ad]

-10 -5 0 5 10Rotation of MW1 or MS1 [mdeg]

-10 -5 0 5 10Rotation of MW1 or MS1 [mdeg]

-10 -5 0 5 10Rotation of MW1 or MS1 [mdeg]

-10 -5 0 5 10Rotation of MW1 or MS1 [mdeg]

Red curve: PDCW1Black curve: PDCS1

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Modulation bench

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Test setup

• Use of vacuum compatible components (free of grease)

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Longitudinal displacement

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Pitch

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Yaw

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Blind test

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Blind test

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Next steps

• Stabilisation loops– Amplitude stabilisation @ 20 kHz– Optical pathlength difference stabilisation

• Bond optics• Use CDS via phasemeter interface• Install final setup inside vacuum envelope• Calibrate signals• Table actuation• Reach design sensitivity