GEO‘s experience with Signal Recycling Harald Lück Perugia,

~600m MPR MSR Dual Recycling in GEO600

Output Mode Cleaner Michelson Interferometer MHz MHz Differential arm length: (gravitational wave signal) heterodyne detection Schnupp modulation Signal-Recycling control: separate modulation frequency reflected beam from beam splitter AR coating Michelson Length Control

SR / PR cavity data f-mod MHz # of FSRsFSR kHz LmLm PR SR tuning ΔL = 93 mm

Output Mode Cleaner Michelson Interferometer MHz MHz Problems with SR Error- Signal:  Small catching range  large influence of MI-deviation from dark fringe. Michelson Length Control

Acquisition signal for SRM SRM tuning [nm] Signal Amplitude [Arb.] 2.5 kHz 0 kHz 5 kHz

Output Mode Cleaner Michelson Interferometer MHz MHz Michelson Length Control ~ ~ -C

Tunable Optical Gain ( Hz) Amplitude [V/m]

Tuning of the SR cavity Tuning is automated using a Labview programme SR tuning parameters: SR modulation frequency SR demodulation phase SR servo gain MI demodulation phase MI servo gain MI AA servo gain

Resonance conditions of Control SBs in SR cavity MI SB SR SB 119 FSR SR 119 FSR PR 72 FSR SR 72 FSR PR 72 FSR SR 72 FSR PR 119 FSR SR 119 FSR PR 119 FSR SR 119 FSR PR 72 FSR SR 72 FSR PR 72 FSR SR 72 FSR PR 119 FSR SR 119 FSR PR

Enhanced peak 1kHz tuning Amplitude [V/m]

Dark port contrast / Mode healing ~ 1 % < % Power rec. MI. without therm. compensation Power rec. MI with therm. compensation Dual rec. MI with therm. compensation -Ratio of carrier light power at dark port / power incident on beamsplitter ~ 0.05% (SB-dominated, 2% MSR) Power inside PR cavity increases from PR to DR mode by 40 %.

Dual Recycled Performance Stable locks at desired tuning frequency with durations of up to 121h. Tuning frequencies 200 – 5000 Hz. High duty cycle in extended data taking periods ( ~97% during S4, i.e. 4 weeks)

Output Mode Cleaner Michelson Interferometer MHz MHz Differential arm length: (gravitational wave signal) heterodyne detection Schnupp modulation Signal-Recycling control: separate modulation frequency reflected beam from beam splitter AR coating 2 EP Quadratures Q P 90°

Uncalibrated Michelson Error Points P Q

On-line optical TF measurements actuator optical CAL P and Q

Optical&Electronic Gain

Calibration

Calibrated EP Quadrature Signals h [1/sqrt(Hz)]

Combining h P (t) and h Q (t) Create filters from noise floor estimates h(t) = Pfilter{h P (t)} + Qfilter{h Q (t)}  PP  QQ  PQ

Combining h P (t) and h Q (t) – results h [1/sqrt(Hz)] Get the best of h P and h Q plus a little extra!

Optical Spring Radiation pressure causes a tuning- dependant force onto cavity mirrors in detuned cavities. From LIGO-P R The dashed curve shows the radiation pressure on the cavity mirror as a function of the detuning from resonance. The solid curve shows the derivative of the optical force, i.e. the optical spring constant. Positive displacement corresponds to increasing the cavity length. The circulating power on resonance is 60 W. The cavity finesse was 380. The oscillator had a mass of approximately 1.2 g, a measured resonance frequency of 303 Hz, a Q of order 3000 (limited by gas damping), and an inferred mechanical spring constant of 2800 Nm−1. longer shorter

Optical spring in GEO600 for different intra-cavity powers … Leistungen

Optical spring for GEO600 for different MSR positions … MSR Positionen P=10kW

Summary tuneable response mode healing GW info in both quadratures more complex SB throughput / noise TFs optical Spring needs to be taken into account detailed numeric simulations + understanding required for advanced detectors

?Questions?

GEO600 layout (S4 values) 1.5 kW T=900ppm

Mode healing or SB enhancement? Check which part of the intra cavity power enhancement comes from the control sidebands becoming resonant inside the SR cavity We get an enhancement of intracav power between PR and SR350Hz of 3.4/2.4 a.u. Sideband power inside SR? Behind MSR say 50mW -> 2W in front, so the resonant sidebands do not contribute to the power enhancement

Theoretical Noise budget