Development of Phase Camera for Advanced Virgo (Experimental part) Kazuhiro Agatsuma Martin van Beuzekom, Mesfin Gebyehu, Laura van der Schaaf, Jo van den Brand National institute for subatmic physics, the Netherlands 15/Dec./2015 Amsterdam Sciencepark1

Amsterdam Sciencepark2 Laser Interference Fringe Beam splitter Mirror Lens Screen Detection of GW by an interferometer Michelson Interferometer ・ Long arms are better ・ Mirrors are suspended => Free falling mass ・ Controlled by actuators => Keeping resonance by Seiji Kawamura Black holes Neutron stars

park3 World network of GW detectors LIGO GEO600 Virgo INDIGO （ in preparation ） State of Washington (4km) State of Louisiana (4km) Competition => Cooperation KAGRA (in construction) (3km) (600m) Hannover Pisa Livingston Parish Hanford Kamioka

Virgo Amsterdam Sciencepark4 Large scale (3 km) gravitational wave detector in Europe (Collaboration between Italy, France, Netherlands, Poland, and Hungary) (Italy, Pisa) [ Upgrade Virgo => Virgo+ arXiv: v1 [physics.ins-det] 22 Nov 2014 => Advanced Virgo (AdV)

Operation of GW detector Amsterdam Sciencepark5 Laser Input Mode Cleaner Output Mode Cleaner Photo detector Dual recycled Fabry-Perot Michelson Interferometer BS Signal recycling mirror Power recycling mirror Control mirror position and angle => Modulation-Demodulation method (Pound–Drever–Hall technique) => Beat signals of sidebands EOM fpfp Fabry-Perot Cavity: ~ km fi+fp fi+fp fi－fp fi－fp fifi sideband

Marginally stable recycling cavity Amsterdam Sciencepark6 AdV uses marginally stable recycling cavity Problem: Degeneration of higher order modes (HOMs) (Reduction of sideband power by aberration of mirrors)  Control becomes unstable Aberrations  Thermal lensing  Substrate inhomogeneities  Surface shape errors Solution: Thermal Compensation System (TCS) *Sensor: Phase camera *Actuator: CO 2 laser with compensation plates ITM BS PRM ITM Pick-off Wave front sensor CO2 laser Compensation plate

Phase Camera Frequency selective wave front sensor  Heterodyne detection  Beam scanning with pin-hole detection Amsterdam Sciencepark7 Test beam (with PM: f p ) Reference beam (Frequency shift by f H ) Pin-hole Scanner BS Demodulation f H, f H +f p, f H -f p I Q Mapping of amplitude and phase EOM IFO (Pick-off mirror in IFO) PM for IFO fH fH fp fp AOM

Prototype test at Nikhef Amsterdam Sciencepark8 EOM AOM Laser PD Scanner Integrated performance is being tested

Prototype test at Nikhef Amsterdam Sciencepark9 Each sideband is selective EOM - Current setup - Test beam: Phase modulator (EOM), DC MHz Reference beam: Fiber coupled AOM, 80 MHz Scanner: PZT scanner (S334, PI), ~1 kHz Photo-detector : FCI-InGaAs-55, φ55um DSP: –Fast ADC/FPGA board: 500MHz Clock Wavelength 1064 nm

*Tilt angle range: 50 mrad (±25 mrad)  Necessary distance btw. PD and scanner: 7 cm (including projection effect of 45°) Scanner (PZT scanner) Amsterdam Sciencepark10 7 cm ~ PD 5 mm5 mm [Requirements]  Scanning area: 5 mm  Test beam size: w = 833 um  Resolution: 100 x 100 pixels  1 image / second *Frequency response  Max. ~1kHz (20 images/sec.) *Scanning pattern  Archimedes' spiral  50 turns

Photo detector Amsterdam Sciencepark11 DC output and RF TIA: HITTITE 799LP3E 10 kOhm, DC – 700MHz 46 nV/rtHz output noise (spec) = 4.6 pA/rtHz input referred Shot noise limited if I diode > ~66 uA FCI-InGaAs-55 Active area diameter = 55  m (pin-hole) NEP 2.66e-15 W/rtHz Flat window, AR coated [VIR-0439A-13] A low noise PD has been developed at Nikhef Flat response up to 700 MHz

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) –  = ~0.3 mRad at 211 MHz ADC fh fh +/- f1..f5 Hann* cosine LUT 16k Hann* sine LUT 16k PD in atan I Q Q I  11x ‘DFT-slice’ cntr 0..N-1 sample clock power to DAQ block fh +/- f1..f5 f1..f5 Amsterdam Sciencepark [VIR-0439A-13]

Mapping result Test beam: 7 MHz PM An ideal phase should be identical between carrier and sidebands  Subtraction of those shows aberration map  The residual phase (noise performance) meets the requirement in an area of the test beam size (833 um) Amsterdam Sciencepark13 CarrierUpper sidebandLower sideband Amplitude Phase Cross section of a residual phase subtraction [Carr-USB] (corresponding length) Requirement: 2 x m

Setup plan in AdV Amsterdam Sciencepark14 : Arm cavity control (common) : SRC : PRC : Support for f1 : Input MC Phase camera will be placed on three detection ports PC1: Input beam [f1 - f5] PC2: Power recycling cavity [f1, f4] PC3: Output beam [f2] Five sidebands will be used Reference beam EOM IMC OMC PC1 PC2 PC3 CO2 laser AOM Laser

Installation in AdV Amsterdam Sciencepark15 Pick-off laser benchPC1 Current pick-off power: 50 mW (before AOM)  13mW is obtained by direct connection to PC1 (6.5 Larger loss than expected (under investigation)

Obtained RF beat signals MHz ・ RF beat signals have been obtained ・ The noise of 78 MHz moves around 80 MHz (cross talk by long cable???) Commissioning at the site is ongoing Amsterdam Sciencepark

Summary Phase camera –Developed for monitoring sidebands and aberrations in a GW detector –frequency selective observation is possible Prototype test at Nikhef –Clear images have been obtained –Total acquisition time and layout are limited by the scanner performance (distance between the PD and scanner should be more than 7 cm) –We have reached the required sensitivity of 2x10 -9 m –Detailed noise investigation is in progress Installation in Advanced Virgo –Three phase cameras will be installed –Installation of PC1 is in progress Amsterdam Sciencepark17