1. 1 Frequency Noise in Virgo by Matt Evans

2. 2 The Actors  Noise Sources  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

3. 3 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

4. 4 Sources: Seismic Excitation

5. 5 Sources: IB transfer function  Dihedron resonace at 80Hz

6. 6 Sources: Actuator Noise  Dihedron resonace at 80Hz  Couples also through offsets (“FmodErr”)

7. 7 Frequency Servo Fast Loop 250kHzSSFS 25kHz MC path 100Hz

8. 8 Servo: Fast Loop  Noise properties not known

9. 9 Servo: SSFS

10. 10 Servo: SSFS

11. 11 Servo: MC path

12. 12 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

13. 13 Coupling to the Dark Fringe B1 Shot Noise B5 Shot Noise Line match Feature match ALL VERY ROUGH!!!

14. 14 Left to be Done  Tune SSFS  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?)