1. 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/2014
TIPP at Amsterdam
2014/June/4

2. Contents Phase 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
2014/June/4

3. 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 waves y z x
2014/June/4

4. Gravitational wave detector
Michelson Interferometer y
Fabry-Perot Michelson Interferometer
Power recycled Fabry-Perot Michelson Interferometer x
Dual recycled Fabry-Perot Michelson Interferometer
Power recycling
mirror
Laser
EOM BS
Fabry-Perot
Cavity fp
Signal recycling
mirror
Input Mode
Cleaner
Output Mode Cleaner
Modulation-Demodulation
(Pound–Drever–Hall technique)
is used to operate IFO
(control position and angle)
Photo detector
2014/June/4

5. VIRGO Nikhef contributes to VIRGO
(Collaboration between France, Italy, Netherlands, Poland and Hungary)
Upgrade
VIRGO => advanced VIRGO (AdV)
(Italy, Pisa) [
Worldwide competition to the first detection
LIGO (USA)
KAGRA (Japan)
After the first detection
World competition => World corroboration
2014/June/4

6. Marginally stable recycling cavity
VIRGO uses marginally stable recycling cavity
Degeneration of higher order modes (HOMs)
(Sideband power reduction can easily happen by aberration of mirrors)
Control becomes unstable
Aberrations
Thermal lens
Substrate inhomogeneities
Surface shape errors
ITM
CO2 laser
Wave front sensor
PRM
ITM BS
Pick-off
Solution: Thermal Compensation System (TCS)
Sensor: Phase camera, Actuator: CO2 laser with compensation plate
2014/June/4

7. Phase Camera Frequency selective wave front sensor
Heterodyne detection
Pin-hole scanning
IFO
(Pick-off mirror in IFO)
PM for IFO
EOM
Test beam
(with PM: fp) fp BS
AOM
Demodulation
fH, fH+fp, fH-fp
Reference beam
(Frequency shift by fH) fH I
Scanner Q
Pin-hole
Mapping of amplitude and phase
2014/June/4

8. Setup plan in AdV Phase camera will be placed on three ports
PC1: Input beam [f1 - f5]
PC2: Power recycling cavity [f1, f4]
PC3: Output beam [f2]
PC1
CO2 laser
PC2
EOM
IMC
PC3
: Arm cavity control (common)
: SRC
: PRC
: Support for f1
: Input MC
OMC
Five sidebands will be used
2014/June/4

9. Setup plan in AdV Frequency shifter: Fiber coupled AOM
PC1: Input beam (Injection bench)
PC2: Power recycling cavity (B4)
PC3: Output beam (B1p)
2014/June/4

10. Prototype test at Nikhef
- 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
2014/June/4

11. Prototype test at Nikhef
Laser
EOM
AOM
Galvanometer PD
2014/June/4

12. Mapping result (preliminary)
Carrier
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!
Test
Reference
USB
2014/June/4

13. Scanning pattern (Archimedes' spiral)
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 mm
Test 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)
2014/June/4

14. Scanner (PZT scanner) ~300 Hz 5 mm PD 20 cm Tilt angle range:
50 mrad (±25 mrad)
to scan 5 mm range,
a half a maximum voltage is necessary with 20 cm distance
The quickest operation is 300 Hz
2014/June/4

15. Photodiode board
New PD has been developed at Nikhef (close to completion)
Flat response up to 700MHz
FCI-InGaAs-55
Active area diameter = 55 mm (pin-hole)
NEP 2.66e-15 W/rtHz
Flat window, AR coated
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
(VIR-0439A-13)
2014/June/4

16. Digital demodulation board
ADC fh
fh +/- f1..f5
Hann*
cosine
LUT 16k
sine
PD in
atan I Q Df
11x ‘DFT-slice’
cntr
0..N-1
sample
clock
power
to DAQ
block
f1..f5
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
(VIR-0439A-13)
2014/June/4

17. Optical layout design (PC1)
z=0
(※) preliminary design
Optical layout is in progress
2014/June/4

18. Summary and Plan Summary
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
2014/June/4