1. LIGO-G0900670-v2 Form F0900040-v1 Advanced LIGO1 SCATTERED LIGHT CONTROL in ADVANCED LIGO Michael Smith LIGO Laboratory Caltech, Pasadena, CA

2. LIGO-G0900670-v2 Form F0900040-v1 LIGO II2 Scattered Light Displacement Noise Theory Min Gravity Wave Signal Scattered Light Requirement: »Phase Shift due to motion of surface »Noise

3. LIGO-G0900670-v2 Form F0900040-v1 LIGO II3 Stray Light Design Requirement <1/10 of the thermal noise limit strain

4. LIGO-G0900670-v2 Form F0900040-v1 LIGO II4 Total Scattered Light Displacement Noise from Multiple Sources, m/rtHz Sources Are Random, Add in Quadrature Scattered Light Transfer functions

5. LIGO-G0900670-v2 Form F0900040-v1 LIGO II5 Scattered Light Transfer Functions from FFT simulation LIGO T060073 Hiro Yamamoto Worse scatter paths

6. LIGO-G0900670-v2 Form F0900040-v1 LIGO II6 Scattered Injection Points

7. LIGO-G0900670-v2 Form F0900040-v1 LIGO II7 Scattered Power into IFO Scattered power depends upon: »Incident power hitting scattering surface, W »Bidirectional Scatter Distribution Function of scattering surface, BRDF, sr^-1 »Solid angle subtended by the mode inside IFO arm, sr »Relative area ratio of IFO mode area to the area of incident beam waist »Transmissivity of optical path from scatter surface to the injection point

8. LIGO-G0900670-v2 Form F0900040-v1 LIGO II8 Measuring BRDF

9. LIGO-G0900670-v2 Form F0900040-v1 LIGO II9 Cleanliness Is Next To Godliness Dust particles scattering light on the sample surface!

10. LIGO-G0900670-v2 Form F0900040-v1 LIGO II10 Example Of BRDF Data

11. LIGO-G0900670-v2 Form F0900040-v1 LIGO II11 Motion Of Scattering Surface, m/rtHz

12. LIGO-G0900670-v2 Form F0900040-v1 LIGO II12 Scattered Light Control Suspended Output Faraday Isolator from Dark-port Signal to Gravity Wave Detector Eddy current damping magnets BS for squeezed light injection

13. LIGO-G0900670-v2 Form F0900040-v1 LIGO II13 Output Faraday Isolator Scatter Displacement Noise Damping to frame Self damping

14. LIGO-G0900670-v2 Form F0900040-v1 LIGO II14 Other Examples Arm Cavity Baffle Wide-angle Baffle Cavity Beam Dump Damped suspension Test mass

15. LIGO-G0900670-v2 Form F0900040-v1 LIGO II15 Modeling Of Ghost Beams Modeling with ZEMAX: beam splitter chamber—ghost beams from internal reflections in the wedged compensation plate next to Input Test Mass (ITM) BS elliptical baffle from ITMX

16. LIGO-G0900670-v2 Form F0900040-v1 LIGO II16 Putting It All Together Scattered Light Meets Requirement!! Total Scatter Requirement Thermal noise