SCATTERED LIGHT CONTROL in ADVANCED LIGO Michael Smith

SCATTERED LIGHT CONTROL in ADVANCED LIGO Michael Smith LIGO Laboratory Caltech, Pasadena, CA LIGO-G 0900670 -v 2 Advanced LIGO Form F 0900040 -v 1

Scattered Light Displacement Noise Theory l Min Gravity Wave Signal l Scattered Light » Noise » Phase Shift due to motion of surface l Requirement: LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Stray Light Design Requirement l <1/10 of thermal noise limit strain LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Total Scattered Light Displacement Noise from Multiple Sources, m/rt. Hz l Sources Are Random, Add in Quadrature l Scattered Light Transfer functions LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Scattered Light Transfer Functions from FFT simulation Worse scatter paths LIGO T 060073 Hiro Yamamoto LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Scattered Injection Points LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Scattered Power into IFO l 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 LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Measuring BRDF LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Cleanliness Is Next To Godliness l Dust particles scattering light on the sample surface! LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Example Of BRDF Data LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Motion Of Scattering Surface, m/rt. Hz LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Scattered Light Control Suspended Output Faraday Isolator BS for squeezed light injection from Dark-port Signal to Gravity Wave Detector Eddy current damping magnets LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Output Faraday Isolator Scatter Displacement Noise Damping to frame Self damping LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Other Examples Damped suspension Test mass Arm Cavity Baffle Wide-angle Baffle Cavity Beam Dump LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

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) elliptical baffle BS from ITMX LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1

Putting It All Together Scattered Light Meets Requirement!! Thermal noise Total Scatter Requirement LIGO-G 0900670 -v 2 LIGO II Form F 0900040 -v 1