Transcript No Slide Title

SCATTERED LIGHT CONTROL
in
ADVANCED LIGO
Michael Smith
LIGO Laboratory
Caltech, Pasadena, CA
LIGO-G0900670-v2
Advanced LIGO
1
Form F0900040-v1
Scattered Light Displacement Noise
Theory

Min Gravity Wave Signal

Scattered Light
Vnoise SNXXX
 SN PSNi
» Noise
» Phase Shift due to motion
of surface

Vsignal DARML
  hmin P0
SNi 
4  xs

1
Requirement: SNXXX  SN  PSNi   DARM  L h min. P0
10
LIGO-G0900670-v2
LIGO II
2
Form F0900040-v1
Stray Light Design Requirement

<1/10 of the thermal noise limit strain
LIGO-G0900670-v2
LIGO II
3
Form F0900040-v1
Total Scattered Light Displacement
Noise from Multiple Sources, m/rtHz

Sources Are Random, Add in Quadrature
2
 SNXXX 4  xs PSNi
1


  L hmin
 DARM 
P0 
10

i 1
n


Scattered Light Transfer functions
TF  
SNXXX
DARM
LIGO-G0900670-v2
LIGO II
4
Form F0900040-v1
Scattered Light Transfer Functions
from FFT simulation
Worse scatter
paths
LIGO T060073 Hiro Yamamoto
LIGO-G0900670-v2
LIGO II
5
Form F0900040-v1
Scattered Injection Points
LIGO-G0900670-v2
LIGO II
6
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
2
PSNi Pin BRDF  
wIFO
2
T
wSN
LIGO-G0900670-v2
LIGO II
7
Form F0900040-v1
Measuring BRDF
LIGO-G0900670-v2
LIGO II
8
Form F0900040-v1
Cleanliness Is Next To Godliness

Dust particles scattering light on the sample surface!
LIGO-G0900670-v2
LIGO II
9
Form F0900040-v1
Example Of BRDF Data
BRDF of Oxidized SS, P-pol
1.00E-01
1.00E-02
polished--no oxide
BRDF (sr^-1)
1 oxide layer
2 oxide layers
3 oxide layers
1.00E-03
4 oxide layers
unpolished, 4 oxide layers
1.00E-04
1.00E-05
0
10
20
30
40
50
60
Angle, deg
LIGO-G0900670-v2
LIGO II
10
Form F0900040-v1
Motion Of
Scattering Surface, m/rtHz
LIGO-G0900670-v2
LIGO II
11
Form F0900040-v1
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-G0900670-v2
LIGO II
12
Form F0900040-v1
Output Faraday Isolator
Scatter Displacement Noise
10
Displacement [m/rtHz]
10
10
10
10
10
-18
AOS Req
Faraday Scatter1
Faraday Scatter0
-20
-22
-24
-26
Damping to frame
Self damping
-28
10
1
10
2
10
3
10
4
Frequency [Hz]
LIGO-G0900670-v2
LIGO II
13
Form F0900040-v1
Other Examples
Damped
suspension
Test mass
Arm Cavity
Baffle
Wide-angle
Baffle
Cavity Beam
Dump
LIGO-G0900670-v2
LIGO II
14
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)
elliptical
baffle
BS
from ITMX
LIGO-G0900670-v2
LIGO II
15
Form F0900040-v1
Putting It All Together
Scattered Light Meets Requirement!!
10
10
Thermal
noise
10
Displacement [m/rtHz]
10
10
10
10
10
10
10
10
-18
Total Scatter
-19
Thermal Noise
AOS Req
Total Scatter
Faraday Scatter
AC Baf
AC Baf Wide Angle
Manifold Wall Wide Angle
ITM GBAR1 BD
ITM GBAR3 BD
ITM GBHR3 ARM
BS GBHR3X ARM
BS GBAR3P BD
BS GBHR3P BD
ITMY HARTMANN BS TRANS
ITMX HARTMANN VIEWPORT
SRM Total
SR2 Total
Requirement
-20
-21
-22
-23
-24
-25
-26
-27
-28
10
1
LIGO-G0900670-v2
10
2
10
3
10
4
Frequency [Hz]
LIGO II
16
Form F0900040-v1