Higher order Laguerre-Gauss modes in future gravitational wave detectors
Phase camera development for gravitational wave detectors
description
Transcript of Phase camera development for gravitational wave detectors
Phase camera development for gravitational wave detectors
Kazuhiro Agatsuma
Martin van Beuzekom, David Rabeling, Guido Visser, Hans Verkooijen, Wilco Vink, Jo van den Brand
4th/June/2014TIPP at Amsterdam
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ContentsPhase camera is prepared for Advanced VIRGO
• Background– Gravitational waves– GW detector– VIRGO– Marginally stable power recycling cavity
• Phase camera– Principle– Setup plan in AdV
• Prototype experiment at Nikhef• Selection of components• Summary and plan
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Gravitational waves
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x
yz
Gravitational waves
Predicted by A. Einstein (1916)Nobody detect it directly yet
Indirect evidence¨ Hulse and Taylor pulsar (1974)
=> Nobel prize (1993)¨ BICEP2 (2014 in discussion)
Direct observations will make a new method to observe universe¨ Binary neutron star¨ Black hole¨ Super nova¨ Inflation¨ Unknown source¨ etc…
¨ General relativity¨ Beginning of universe
Gravitational wave detector
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Laser
Input ModeCleaner
Output Mode Cleaner
Photo detector
y
x
Michelson InterferometerFabry-Perot Michelson InterferometerPower recycled Fabry-Perot Michelson InterferometerDual recycled Fabry-Perot Michelson Interferometer
Fabry-PerotCavity
BS
Signal recycling mirror
Power recycling mirror
Modulation-Demodulation(Pound–Drever–Hall technique)is used to operate IFO(control position and angle)
EOM
fp
VIRGO
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Nikhef contributes to VIRGO(Collaboration between France, Italy, Netherlands, Poland and Hungary)
UpgradeVIRGO => advanced VIRGO (AdV)
Worldwide competition to the first detection¨ LIGO (USA)¨ KAGRA (Japan)
After the first detectionWorld competition => World corroboration
(Italy, Pisa)[http://www.ego-gw.it/public/about/welcome.aspx]
Marginally stable recycling cavity
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VIRGO uses marginally stable recycling cavityÞ Degeneration of higher
order modes (HOMs)(Sideband power reduction can easily happen by aberration of mirrors)Þ Control becomes unstable
Aberrations¨ Thermal lens¨ Substrate inhomogeneities¨ Surface shape errors
Solution: Thermal Compensation System (TCS) Sensor: Phase camera, Actuator: CO2 laser with compensation plate
ITMBSPRM
ITM
Pick-off
Wave front sensor
CO2 laser
Phase CameraFrequency selective wave front sensor¨Heterodyne detection¨Pin-hole scanning
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Test beam(with PM: fp)
Reference beam(Frequency shift by fH)
Pin-hole
Scanner
BSDemodulationfH, fH+fp, fH-fp
IQ
Mapping of amplitude and phase
EOM
IFO(Pick-off mirror in IFO)PM for IFO
fH
fpAOM
Setup plan in AdV
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: Arm cavity control (common)
: SRC
: PRC
: Support for f1
: Input MC
EOM
IMC
OMC
PC1PC2
PC3
CO2 laser
Phase camera will be placed on three portsPC1: Input beam [f1 - f5]PC2: Power recycling cavity [f1, f4]PC3: Output beam [f2]
Five sidebands will be used
Setup plan in AdV
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Frequency shifter: Fiber coupled AOMPC1: Input beam (Injection bench)PC2: Power recycling cavity (B4)PC3: Output beam (B1p)
Prototype test at Nikhef
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- Current setup -• Test beam:
Phase modulator (EOM): DC -> 250 MHz
• Reference beam: Frequency shift (AOM): 80 MHz
• Scanner: Galvanometer (GVS012)• Photo-detector : New focus 1811 (125 MHz)• DSP:
– LAPP fast ADC/FPGA board (400MHz Clock)– AdV Real-time system signal processing
Each sideband is selective
Prototype test at Nikhef
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AOM
EOM
Laser
Galvanometer
PD
Mapping result (preliminary)• Test beam: 10MHz PM• Power ratio (test beam and
reference beam) is not optimized here
=> Calculation of SNR using actual parameters is in progress
• The phase between carrier and sidebands should be identical in the ideal IFO
=> Subtraction of those shows aberration map!
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Carrier
USB
Test Reference
Scanning pattern (Archimedes' spiral)
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32 x 32 pixels: 16 Hz 128 x 128 pixels: 64 Hz 256 x 256 pixels: 128 Hz
In the case of the total acquisition time of 1 second to make one pattern(According to a simulation, a total acquisition time of at least 2-5 s [0.03 s] is necessary in order to keep sufficient precision of the phase measurement)Standard aperture diameter: 5 mmTest beam size: w = (2.5) / 3 = 833 um
Quickest acquisition is 0.25 s (128 x 128 pixels, 256 Hz) with our scanner(Requirement: 100 x 100 pixels)
Scanner (PZT scanner)
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Tilt angle range: 50 mrad (±25 mrad)
Þ to scan 5 mm range,a half a maximum voltage is necessary with 20 cm distanceÞ The quickest operation is 300 Hz
~300 Hz
20 cm
PD5 mm
Photodiode board
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• DC output and • RF TIA: HITTITE 799LP3E• 10 kOhm• DC – 700MHz• 46 nV/rtHz output noise (spec)• = 4.6 pA/rtHz input referrred• Shot noise limited if Idiode > ~66 uA
• FCI-InGaAs-55• Active area diameter = 55 mm (pin-hole)• NEP 2.66e-15 W/rtHz• Flat window, AR coated
(VIR-0439A-13)
New PD has been developed at Nikhef (close to completion)Flat response up to 700MHz
Digital demodulation board
• Digital Demodulation at 11 (fixed) frequencies (fh+/f1..f5) in parallel• 14 bit ADC at 500 MS/s + Xilinx Virtex-7 FPGA• Measure phase (and power) using 16k samples per ‘pixel’
– can measure 32 k ‘pixels’ per second, frequency resolution ~30 kHz• Best resolution when using external ref. frequencies (i.e. diff. phase measurement)
– s = ~0.3 mRad at 211 MHz
ADC
ADCfh
fh +/- f1..f5
Hann*cosine
LUT 16k
Hann*sine
LUT 16k
PD in atan
I
Q
atan
Q
I
Df
11x ‘DFT-slice’
cntr0..N-1
sampleclock
power
to DAQblock
fh +/- f1..f5f1..f5
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(VIR-0439A-13)
Optical layout design (PC1)
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z=0 ( ) preliminary design※
Optical layout is in progress
Summary and PlanSummary• Phase camera can observe wave fronts for each PM sideband
=> Useful monitor for TCS in Virgo• Prototype experiment is on going
– Component selection has done– High speed PD and digital board are being prepared at Nikhef
Plan (in progress)• SNR calculation using actual parameters• Optical layout drawings
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