Frequency Noise in Virgo by Matt Evans
The Actors Noise Sources Frequency Servo Coupling to the Dark Fringe Input Mode Cleaner length noise Sensing noise on IMC lock Frequency Servo Servo topology Gain limitations Sensing noises Coupling to the Dark Fringe Common Mode Rejection Ratio Fluctuations
Sources: IMC Length Excitation Injection bench alignment sensor noise below 15Hz Seismic excitation between 15 and 20Hz also possibly higher… problem with suspension? Actuator noise IB coil-driver/DAC noise Mode cleaner end mirror DAC noise
Sources: Seismic Excitation
Sources: IB transfer function Dihedron resonace at 80Hz
Sources: Actuator Noise Dihedron resonace at 80Hz Couples also through offsets (“FmodErr”)
Frequency Servo MC path 100Hz Fast Loop 250kHz SSFS 25kHz
Servo: Fast Loop Noise properties not known
Servo: SSFS
Servo: SSFS
Servo: MC path
Coupling to the Dark Fringe Line match at 444 and 1111Hz Modulation spreads line power The coupling fluctuates quickly Coherent analysis is difficult Noise projection is approximate
Coupling to the Dark Fringe Line match Feature match B1 Shot Noise B5 Shot Noise ALL VERY ROUGH!!!
Left to be Done Tune SSFS Understand fast loop noise Increase gain between 1 and 5kHz Improve phase margin by removing unnecessary delay in cables, OpAmps, ... Understand fast loop noise Electronics Scattering on external bench ND filters, clipping Other ideas? Stabilize coupling (alignment?)