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The AEI 10m Prototype Interferometer
Tobias Westphal for the AEI 10 m Prototype team
http://10m-prototype.aei.uni-hannover.de
DPG spring meeting, March 2011
Why to build another PT
Maximal overlap with GEO-HF subsystems
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Develop and prove as many of the techniques needed for gravitational wave detector
upgrades as possible (e.g. laser, digital control infrastructure)
Provide training for people who will install upgrades to and run GEO-HF
Ultra-low displacement-noise test environment
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•
•
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To probe at and beyond the Standard Quantum Limit (SQL)
equivalent Heisenberg limit for 100 g test masses
Thermal noise interferometer
Other experiments within QUEST (for e.g. LISA or GRACE follow on)
Entanglement of macroscopic test masses (a bit further down the road…)
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What is the SQL
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SQL interferometer layout
Optional:
Signal recycling
~8 W @ 1064 nm fiber coupled
10 m Fabry-Perot arm cavity
Finesse ca. 700
Tap off
~130 mW
Optional:
Power recycling
100 g Mirrors
monolithic silica suspensions
Frequency
reference cavity
Length: 12 m
Finesse: ca. 7500
Triple pendulum suspension
Mirror mass: 860 g
Anti-resonant
Fabry-Perot cavity
as compound end mirror
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Squeeze-in tanks
Learn from experience!
Earlier days (GEO600 design):
• Not very versatile
• REALLY uncomfortable
to work in
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Walk-in tanks
100 mm flanges
to fit feed throughs
600 mm flanges
to fit viewports
Walk-in door
100 mm flanges
to fit feed throughs
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Ultra-high vacuum system
Tubes:
1.5 m Ø
Tanks:
3.4 m tall
3m •
Ø
• 100 m³ Volume
• 22 t stainless steel
• 170 l/s screw pump (roughing)
• 2x 2000 l/s turbo pump (main)
• 2x scroll pump (backing & differential)
10-6mbar after
about 12 hours
• Metal gaskets below 600 mm
• Double O-ring differentially pumped
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Sliced open
• Optical benches in the tanks
• Passive seismic isolation
• Active inter table stabilisation
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Table subsystems
Accelerometer
Vertical
motorized
blade
Inverted
pendulum
Geometric
antispring
Optical table
Filter support
Base plate
LVDT / Actuator
Horizontal
motorized
blade
Tilt stabilisation
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GAS filter (vertical isolation)
Top view
Side view
Featuring
• very soft potential → large isolation
• Huge loading capabilities
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Estimated motion
micro-seismic
10-5
Ground
Horizontal
Vertical
10-6
anthropogenic
Displacement [m/√Hz]
10-7
10-8
10-9
10-10
10-11
60 dB
10-12
10-13
10-14
70 dB
10-2
10-1
100
101
102
Frequency [Hz]
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Vertical isolation (measured)
← GAS-resonance frequency ca. 440 mHz
0
-10
Reference Measurement
Transfer function [dB]
without magic wand
-20
Single Magic Wand (SiC)
-30
-40
-50
off-centered
accelerometer
-60
7 dB
-70
-80
shaker structure
-90
1
10
Frequency [Hz]
100
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GAS filter shaker
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GAS filter in action
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Estimated differential motion
10-5
Ground
Horizontal
Vertical
10-6
Displacement [m/√Hz]
10-7
Inter table
10-8
Active isolation
10-9
10-10
Passive
isolation
10-11
10-12
10-13
10-14
10-2
10-1
100
101
102
Frequency [Hz]
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Low freqency active isolation
10-5
Ground
Horizontal
Vertical
10-6
Displacement [m/√Hz]
10-7
Stabilized
inter table
10-8
Active isolation
10-9
10-10
Passive
isolation
10-11
SPI
10-12
Accelerometers
LVDT`s
10-13
10-14
10-2
10-1
100
101
102
Frequency [Hz]
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Suspension platform interferometer
Goal:
• Stabilize inter table motion
• 100 pm/√Hz, 10 nrad/√Hz
@ 10 mHz
Based on LISA Pathfinder experience:
• Heterodyne Mach-Zehnder
interferometer with unequal arm
length (by 23 m)
• Iodine-stabilised Nd:YAG
(frequency noise)
• Optics bonded onto low CTE plate
(thermal drifts)
• Digital signal processing (FPGAs)
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Digital control system
Analog world
• Gives error signals
• Carries actuation out
Digital world
• Based on realtime LINUX
• Runs EPICS software
Experiment
Sensors &
actuators
Front-end
Fieldboxes
ADC/DAC
Signal
conditioning
6 x 32channel
PCI-X
DA/AD & DIO
AA/AI filters
User world
• Changes
• Get data
Workstation
Digital filters
Frame builder
GPS
timing
Storage
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Laser: 35W @ 1064nm
Crystals:
• 3 x 3 x 10 mm3 Nd:YVO4
• 8 mm 0,3 % doped, 2 mm endcap
24 W measurement
TEM00 model
Normalized power
Pump diode:
• 808 nm, 45 W
• 400 µm Ø fiber coupled, NA=0,22
99% in
TEM00
Amplifier:
• 38 W for 2 W seed and 150 W pump
Frequency [FSR]
Nd:YVO4
crystals
Isolator
/2
pump
optics
/4
NPRO
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Mirror suspensions
Frequency reference cavity:
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•
Three horizontal, two vertical stages
850 g per stage (mirror 10 cm x 5 cm)
Steel wires, last stage 55 µm Ø
Local control and alignment control at
uppermost stage
(fast alignment is done at steering mirrors)
Interferometer optics:
• Three horizontal stages, two vertical stages
• 100 g per stage (mirror ca. 2“ x 1“)
• All silica last stage, 4 filaments of 20 µm Ø
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Sensitivity w/o Khalili cavities
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Where does coating noise appear?
Coating noise
Reflectivity
N
N
High reflective coatings have lots of coating layers
(1) Few layers  medium R, low CTN
(2) Many layers  high R, high CTN
Let‘s separate reflectivity and losses!
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Khalili cavity
IETM
EETM
(2n+1) /2
One HR mirror  two mirrors:
1. Medium reflectivity: ca. 50 % (IETM)
2. High reflectivity:
99.99 % (EETM)

Factor 1.6 reduction of coating thermal noise
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Sensitivity w/o Khalili cavities
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Sensitivity with Khalili cavities
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Sensitivity with doping & Khalili
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The team
http://10m-prototype.aei.uni-hannover.de
Ken Strain: Scientific leader
Stefan Goßler: Coordinator
Gerhard Heinzel: LISA/LPF related experiments
Yanbei Chen, Kentaro Somiya, Stefan Danilishin: Experiment design, noise analysis
Roman Schnabel: Squeezing and QND experiments
Harald Lück: Vacuum system and GEO 600 related experiments
Hartmut Grote: Electronics and GEO 600 related experiments
GEO operators: Filter design and construction, environmental monitoring
Andreas Weidner: Electronics design
Kasem Mossavi: Vacuum system and pumps control
Jens Breyer: Mechanical design
Benno Willke, Jan Hendrik Pöld, Christina Bogan: High power laser
Gerrit Kühn, Michael Born, Martin Hewitson: Real time control system
Alessandro Bertolini, Alexander Wanner: Isolation tables
Katrin Dahl: SPI
Fumiko Kawazoe: Frequency reference cavity
Stefan Hild, Sabina Huttner, Christian Gräf: Interferometric sensing & control
Giles Hammond, Tobias Westphal: Monolithic suspensions
Gerald Bergmann: Commissioning
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