1. Frequency Noise in Virgo
by Matt Evans

2. 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

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. Sources: Seismic Excitation

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

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

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

8. Servo: Fast Loop
Noise properties not known

9. Servo: SSFS

10. Servo: SSFS

11. Servo: MC path

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

14. 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?)