ligo commissioning update
DESCRIPTION
LIGO Commissioning Update. LSC Meeting, March 16, 2004 Peter Fritschel. S3: peak sensitivities. S3: reliability & stability. Major Goals and Tasks After S3. Sensitivity Operate at high power: achieve designed optical gain Laser Thermal compensation system (TCS) Output mode cleaner (OMC) - PowerPoint PPT PresentationTRANSCRIPT
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G040066-00-D
LIGO Commissioning Update
LSC Meeting, March 16, 2004
Peter Fritschel
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LIGO I 2G040066-00-D
S3: peak sensitivities
102
103
10-23
10-22
10-21
10-20
10-19
10-18
10-17
Frequency (Hz)
Str
ain
no
ise,
h (
f) (
Hz-1
/2)
H1, 4 Jan 04, 6.5 MpcH2, 30 Nov 03, 0.8 MpcL1, 19 Dec 03, 1.5 MpcSRD Goal (4k)
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LIGO I 3G040066-00-D
S3: reliability & stability
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LIGO I 4G040066-00-D
Major Goals and Tasks After S3
Sensitivity Operate at high power: achieve designed optical gain
Laser Thermal compensation system (TCS) Output mode cleaner (OMC)
Manage noise in auxiliary degrees-of-freedom Finish acoustic mitigation Clean up electronics: RFI mitigation
Reliability & Stability Seismic retrofit at LLO: HEPI Auto-alignment system: all degrees-of-freedom, at full bandwidth Address causes of lock-loss
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LIGO I 5G040066-00-D
Recall: significant improvements between S2 & S3 Problem: acoustical vibrations of optical elements in the output beam path No acoustic peaks left in S3 spectra Acoustic enclosures around AS port sensing tables: ~10x reduction Improvements and simplifications to beam sensing path: ~10x
Original goals: 100x-1000x reduction, reached for H1
5
Acoustic Mitigation
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LIGO I 6G040066-00-D
Acoustic Mitigation (2) Raise the bar at LHO: H1-H2 stochastic b.g. potential
H1 sensitivity now dominated by reflection port table: continue improvement/simplifications of this beam path
Reduce continuous sources: house or move electronics cabinets
New data on lower frequencies: seismic/acoustic HVAC the main source: no easy improvements Investigating ‘floating’ the detection tables on low-frequency mounts
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LIGO I 7G040066-00-D
More environmental effects
Dust in table enclosures Gets stirred up by entries, takes
a while to settle down Causes glitches when it falls
through the beam To be addressed with HEPA
filters, and/or covers over the beam path
Dust monitor at AS port table
1 day
HVAC in-duct heaters Pulsing produces ~1 Hz
sidebands around 60 Hz; couples magnetically to AS_Q
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LIGO I 8G040066-00-D
Optical gain: “10 W” laser
Current input power levels
H1 H2 L1 Design
Mode cleaner input 3.6 W 3.7 W 6 W 8 W
Recycling mirror input 2.3 W 2.6 W 3.6 W 6 W
Plan Get LWE lasers back up to spec: LWE may be able to rebuild for
somewhat higher power, 10 W 12-15 W Diagnose pre-mode cleaner loss (typically 10-15% lost) Diagnose suspended mode cleaner loss (20-30% lost) Input electro-optic modulators: reduce number from 3 to 1
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LIGO I 9G040066-00-D
Thermal Compensation
Over-heat Correction
Inhomogeneous Correction
Under-heat Correction
CO2
Laser
?
ZnSe Viewport Over-heat pattern
Inner radius = 4cm Outer radius =11cm
Cold power recycling cavity is unstable: poor buildup and mode shape for the RF sidebands
ITM thermal lens power of ~0.00003 diopters needed to achieve a stable, mode-matched cavity
intended to be produced by ~25 mW absorbed from 1μm beam
ITM
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LIGO I 10G040066-00-D
Two CO2 lasers installed on H1
To ITM HRsurface
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LIGO I 11G040066-00-D
TCS on the power recycled Michelson: beam images at AS port
No Heating 30 mW 60 mW 90 mW
120 mW 150 mW 180 mW Input beam
Best match
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LIGO I 12G040066-00-D
Full Interferometer Results
A. Lock interferometer at 1 Watt
B. Apply 45 mW Common central heating
C. Increase to 60 mW
D. Increase to 90 mW
E. Turn off TCS
Sideband power gain
25
16.5
8.3
0
A
BC
D
E
Opticalgain
AS_Q gain: increases by 40% doesn’t increase as fast as expected
PRC & MICH (pick-off) gains increase by factor of 4
gain scales as (GSB)2
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LIGO I 13G040066-00-D
Summary of TCS Results
State GSB ----------------------------------------------------------------------------State 2 cold 7.0 State 2 hot (90 mW CO2) 12.5State 2 max (tRM / (1 - rRM rM rITM))2 14 ----------------------------------------------------------------------------State 4 cold 13State 4 warm (0.8W input) 16 State 4 hot (2.3W input, no TCS) 20 State 4 hot (0.8W input, 45mW CO2) 26.5 State 4 max (tRM / (1 - rRM rM))2 30 ----------------------------------------------------------------------------
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LIGO I 14G040066-00-D
Output mode cleaner: motivation
Reduction of AS_I signal Power in orthogonal phase limits the amount of power per AS port
photodetector & AS_I servo is noisy Produced by alignment fluctuations: TEM01/10 modes would be
removed by an OMC
Improvement in shot noise sensitivity Reduction of noise-producing (higher-order mode) power
Potential saturation at 2fm at higher power
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LIGO I 15G040066-00-D
OMC design overview
Cavity finesse30
(maximum mode suppression of 300x)
Cavity round-trip path/bandwidth10 cm / 100 MHz
(keep short/wide to pass SBs on same resonance)
GeometryTriangular ring cavity; fixed spacer with bonded mirrors
g-parameter Approx. 0.4
Mounting & isolationIn-vacuum, single stage
suspension
Locking and controlPZT-mounted end mirror, dither
lock in transmission
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LIGO I 16G040066-00-D
OMC plans
GEO output mode cleaner a good fit for initial testing On loan from GEO for several months
Installation and testing on H1 Beginning mid-April Will be put into the beam path of one of
the AS port detection PDs
AS portbeam
50/50
LSC PD
PZT
T = 10%
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LIGO I 17G040066-00-D
Alignment Control
Continued incremental progress on WFS/QPDs … Goals:
Sufficient gain/bandwidth to reduce power fluctuations to ~1% Turn off optical lever angular control: too noisy Manage WFS/QPD noise coupling to AS_Q
Status, H1 (post-S3 progress) Bandwidth now at 2.2 Hz for all but one WFS: effect not fully characterized Some noise reductions made, still an active issue Initial alignment steps now fully automated
Upcoming Controls software upgrade: sensor input matrix; compensate radiation
torques; compensate for optical gain change WFS feedback to mode cleaner mirrors Beam centering …
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LIGO I 18G040066-00-D
Beam centering Transmission QPDs hold the beam position fixed at the ETMs
Need to independently find the right spot (w/in 1mm of center)
WFS control all mirror angles: only DOF left is the beam position in the corner
New servo: Capture image of beam scatter from BS face Image processing to determine position of
beam center Slow feedback to input telescope to fix BS
beam position
ON
Pitch fbSign fixed
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LIGO I 19G040066-00-D
Auxiliary degrees-of-freedom:small coupling, but very noisy
101
102
10-16
10-15
10-14
10-13
10-12
10-11
10-10
10-9
10-8
Frequency [Hz]
Dis
plac
emen
t [m
/H
z]
MICH Noise
101
102
Frequency [Hz]
PRC NoiseSeismic (h)Seismic (v)ShotDark NoiseRM ElectronicsPRC_ERRPRC
Seismic (h)Seismic (v)ShotDark NoiseBS ElectronicsMICH_ERRMICH
X-cplg to ASQ: 0.01 @100Hz
X-cplg to ASQ: 0.001 @100Hz
Excess noise
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LIGO I 20G040066-00-D
Excess noise: optical gain modulation
Signal (sideband field)·(length deviation)
Intermodulation
Effect of increasing the MICH bandwidth from 10Hz to 50Hz: > 10x lower noise at 40Hz > able to detect higher power pick-off beam for reduced shot noise
Similar noise reduction for PRC, and for the WFS error signals
Reduce these by increasing loop gain
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LIGO I 21G040066-00-D
Impact on noise
102
10-20
10-19
10-18
10-17
10-16
10-15
10-14
10-13
Frequency (Hz)
Dis
pla
cem
ent
no
ise
(m/H
z1/2 )
S3 AS_QS3 auxCurrent AS_QCurrent aux
Low gainHigh gain
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LIGO I 22G040066-00-D
Seismic retrofit at LLO
Currently ~2 weeks into installation
Recent best performance data from LASTI, on a HAM chamber:
10-1
100
101
10-2
10-1
100
Mag
nitu
de (Z C
oeffi
ecen
t = -0.
75)
LASTI HAM: Ground X to Support Table Streckheisen X
Frequency (Hz)
Averaged Signal Off
Loop Gain Limit
Model Prediction
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LIGO I 23G040066-00-D
High-f noise bump: mystery solved
Modulation phase noise appears on demodulation signal (LO) too – no big deal
True at low frequencies, but mode cleaner pole shifts phase of modulation fields – doesn’t cancel out at higher frequencies
Solutions: Low phase noise
crystal oscillator Pass LO through
an electronic filter to equalize paths
RF Oscillator phase noise Mechanism: possibly coupling through the DC AS_I signal
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LIGO I 24G040066-00-D
Miscellaneous
New low-noise D-A converters from Freq. Devices Inc. 30-40 dB lower noise
New Faraday isolator for H2 Larger aperture to reduce clipping Lower absorption for higher power operation
Photon calibrators Reproducing first-article: in place for S4
Phase cameras on all interferometers Introducing a reference field so that any field component can be mapped
Dual ETM transmission photodetectors To handle larger dynamic range with higher power
Upgrade DAQ reflective memory network: higher capacity Micro-seismic feedforward system at LHO
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LIGO I 25G040066-00-D
Major Post-S3 Steps
First ~6 months after S3
L1
► Thermal lens studies
► Seismic upgrade: HEPI installation & commiss.
► Electronics rack relocation
► Thermal comp.
H1
► Manage noise in auxiliary degrees-of-freedom
►Thermal compensation trial
► Wideband WFS control
► Laser power increase
► Output mode cleaner
► Duty cycle
H2 ► Wideband WFS control