Phase camera development for gravitational wave detectors

1. Phase camera development for gravitational wave detectors Kazuhiro Agatsuma Martin van Beuzekom, David Rabeling, Guido Visser, Hans Verkooijen, WilcoVink, Jo van den Brand 4th/June/2014 TIPP at Amsterdam TIPP@Amsterdam

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 TIPP@Amsterdam

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 TIPP@Amsterdam

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 BS Laser EOM 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 TIPP@Amsterdam

5. VIRGO Nikhef contributes to VIRGO (Collaboration between France, Italy, Netherlands, Poland and Hungary) Upgrade VIRGO => advanced VIRGO (AdV) (Italy, Pisa) [http://www.ego-gw.it/public/about/welcome.aspx] • Worldwide competition to the first detection • LIGO (USA) • KAGRA (Japan) • After the first detection • World competition => World corroboration TIPP@Amsterdam

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 ITM PRM BS Pick-off Solution: Thermal Compensation System (TCS) Sensor: Phase camera, Actuator: CO2 laser with compensation plate TIPP@Amsterdam

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 Demodulation fH, fH+fp, fH-fp AOM Reference beam (Frequency shift by fH) fH I Scanner Q Pin-hole Mapping of amplitude and phase TIPP@Amsterdam

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 TIPP@Amsterdam

9. Setup plan in AdV Frequency shifter: Fiber coupled AOM PC1: Input beam (Injection bench) PC2: Power recycling cavity (B4) PC3: Output beam (B1p) TIPP@Amsterdam

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 TIPP@Amsterdam

11. Prototype test at Nikhef Laser EOM AOM Galvanometer PD TIPP@Amsterdam

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 TIPP@Amsterdam

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) TIPP@Amsterdam

14. Scanner (PZT scanner) ~300 Hz 5mm 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 TIPP@Amsterdam

15. Photodiode board New PD has been developed atNikhef (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) TIPP@Amsterdam

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

17. Optical layout design (PC1) z=0 (※) preliminary design Optical layout is in progress TIPP@Amsterdam

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 TIPP@Amsterdam