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Advanced LIGO 1LIGO-G0900670-v2
Form F0900040-v1
SCATTERED LIGHT CONTROLin
ADVANCED LIGO
Michael Smith
LIGO LaboratoryCaltech, Pasadena, CA
LIGO II 2LIGO-G0900670-v2
Form F0900040-v1
Scattered Light Displacement NoiseTheory
Min Gravity Wave Signal
Scattered Light
Requirement:
Vnoise SNXXX SN PSNi
Vsignal DARM L hmin P0
» Phase Shift due to motion
of surfaceSNi
4 xs
» Noise
SNXXX SN PSNi1
10DARM L hmin. P0
LIGO II 3LIGO-G0900670-v2
Form F0900040-v1
Stray Light Design Requirement
<1/10 of the thermal noise limit strain
LIGO II 4LIGO-G0900670-v2
Form F0900040-v1
Total Scattered Light Displacement Noise from Multiple Sources, m/rtHz
Sources Are Random, Add in Quadrature
1
n
i
SNXXX
DARM
4 xs
PSNi
P0
2
1
10L hmin
Scattered Light Transfer functions TFSNXXX
DARM
LIGO II 5LIGO-G0900670-v2
Form F0900040-v1
Scattered Light Transfer Functionsfrom FFT simulation
LIGO T060073 Hiro Yamamoto
Worse scatter paths
LIGO II 6LIGO-G0900670-v2
Form F0900040-v1
Scattered Injection Points
LIGO II 7LIGO-G0900670-v2
Form F0900040-v1
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
PSNi Pin BRDF wIFO
2
wSN2
T
LIGO II 8LIGO-G0900670-v2
Form F0900040-v1
Measuring BRDF
LIGO II 9LIGO-G0900670-v2
Form F0900040-v1
Cleanliness Is Next To Godliness
Dust particles scattering light on the sample surface!
LIGO II 10LIGO-G0900670-v2
Form F0900040-v1
Example Of BRDF DataBRDF of Oxidized SS, P-pol
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
0 10 20 30 40 50 60
Angle, deg
BRD
F (s
r^-1
)
polished--no oxide
1 oxide layer
2 oxide layers
3 oxide layers
4 oxide layers
unpolished, 4 oxide layers
LIGO II 11LIGO-G0900670-v2
Form F0900040-v1
Motion Of Scattering Surface, m/rtHz
LIGO II 12LIGO-G0900670-v2
Form F0900040-v1
Scattered Light ControlSuspended Output Faraday Isolator
from Dark-port Signal
to GravityWave Detector
Eddy current damping magnets
BS for squeezed light injection
LIGO II 13LIGO-G0900670-v2
Form F0900040-v1
Output Faraday Isolator Scatter Displacement Noise
101
102
103
104
10-28
10-26
10-24
10-22
10-20
10-18
Frequency [Hz]
Dis
pla
cem
en
t [m
/rtH
z]
AOS ReqFaraday Scatter1Faraday Scatter0
Damping to frame
Self damping
LIGO II 14LIGO-G0900670-v2
Form F0900040-v1
Other Examples
Arm Cavity Baffle
Wide-angle Baffle
Cavity Beam Dump
Damped suspension
Test mass
LIGO II 15LIGO-G0900670-v2
Form F0900040-v1
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
LIGO II 16LIGO-G0900670-v2
Form F0900040-v1
Putting It All TogetherScattered Light Meets Requirement!!
101
102
103
104
10-28
10-27
10-26
10-25
10-24
10-23
10-22
10-21
10-20
10-19
10-18
Frequency [Hz]
Dis
pla
cem
ent [
m/r
tHz]
Thermal NoiseAOS ReqTotal ScatterFaraday ScatterAC BafAC Baf Wide AngleManifold Wall Wide AngleITM GBAR1 BDITM GBAR3 BDITM GBHR3 ARMBS GBHR3X ARMBS GBAR3P BDBS GBHR3P BDITMY HARTMANN BS TRANSITMX HARTMANN VIEWPORTSRM TotalSR2 Total
Total Scatter RequirementThermal noise
