Frequency Noise in Virgoby Matt Evans

The ActorsNoise SourcesInput Mode Cleaner length noiseSensing noise on IMC lockFrequency ServoServo topologyGain limitationsSensing noisesCoupling to the Dark FringeCommon Mode Rejection RatioFluctuations

Sources: IMC Length ExcitationInjection bench alignment sensor noise below 15HzSeismic excitationbetween 15 and 20Hzalso possibly higher problem with suspension?Actuator noiseIB coil-driver/DAC noiseMode cleaner end mirror DAC noise

Sources: Seismic Excitation

Sources: IB transfer functionDihedron resonace at 80Hz

Sources: Actuator NoiseDihedron resonace at 80HzCouples also through offsets (FmodErr)

Frequency ServoFast Loop 250kHzSSFS 25kHzMC path100Hz

Servo: Fast LoopNoise properties not known

Servo: SSFS

Servo: SSFS

Servo: MC path

Coupling to the Dark FringeLine match at 444 and 1111HzModulation spreads line powerThe coupling fluctuates quickly Coherent analysis is difficultNoise projection is approximate

Coupling to the Dark FringeB1 Shot NoiseB5 Shot NoiseLine matchFeature matchALL VERY ROUGH!!!

Left to be DoneTune SSFSIncrease gain between 1 and 5kHzImprove phase margin by removing unnecessary delay in cables, OpAmps, ...Understand fast loop noiseElectronicsScattering on external benchND filters, clippingOther ideas?Stabilize coupling (alignment?)