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Modeling of the Effects of Beam Fluctuations from LIGO’s Input Optics
Nafis Jamal
Shivanand
Sanichiro Yoshida
Biplab Bhawal
LSC Conference Aug ’05
LIGO-G050443-00-Z
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PART I:
Modeling MMT’s motion and effect on power in the arm cavity
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The SimLIGO model
Power meters
Seismic Motion
Pre-StabilizedLaser
Input Optics
Core Optics
InterferometerSensingControl
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Objective
Study the effect of the fluctuation of the input beam Provide seismic noise to input optics No seismic influence on core optics Study the effect of input beam’s fluctuations
under the following conditions:
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Conditions on Core Optics(Cases)
Note : There is no suspension point motion to any of these mirrors
OptLev
LSC Floor
OptLev
LSC Floor
OptLev
LSC Floor
OptLev
LSC FloorCase 1 : Dead Cavity (No Control) Case 2 : Only LSC on
Case 3 : LSC + OptLev on, Floor off Case 4 : LSC + OptLev on, Floor on
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Conditions on the Input Optics (Runs)
The following table shows the state of different input optics, that has been used to study the four cases mentioned in the last slide
runs MMT1 MMT2 MMT3
1 0 0 0
2 1 0 0
3 0 1 0
4 0 0 1
5 1 1 1
6 0 0 10
0 – no suspension point motion 1 – suspension point motion turned on at 0.7s10 – optic has 10 times larger motion
All Quiet
Only MMT1 moving
Only MMT3 movingbut 10 times larger motion
All IO moving
Only MMT3 moving
Only MMT2 moving
Seismic Noise
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Figure 1: Time series LSC,OptLev (3) LSC,OptLev w/Floor (4)
Lock loss
0.04%
2.20%
0.10%
1.56%
78.81%
1.887%
1.340%
0.112%
0.045%
<0.001%
MMT1
Quiet
MMT2
MMT3
All
MMT3x10
0.4%
0.4%
0.4%
1.24%
1.75%
TEMOO to CO ETMx Trans ETMx Trans
LOCK LOSS
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Findings from Case 3LSC + OptLev
OptLev on » same power in arms as OptLev off» extra noise in DARM error signal
20Hz, 40Hz peaks in both DARM and Opt Lev signals when quiet case subtracted
DARM_ERR for Run 1Case 2 Case 3
40 Hz20 Hz
d-DARM Run 3d-Opt Lev Pitch
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Figure 7: The frequency spectrum of results of Case 3, 4
**Quiet MMT run subtracted
MMT1
MMT2
MMT3
All
Why MMT effect more prominent at 23Hz with floor motion?(Compared to quiet floor case)
Case 3, OptLev Case 4, OptLev w/Floor
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Conclusion (Part I)
When MMT3 experiences 10 times larger suspension point motion, the fluctuation in the input beam increases by about 77% and the LSC fails to keep the arm cavities locked.
Even when LSC works at its best, the maximum mode mismatch due to the input beam fluctuation is directly proportional to the fluctuations in the TEM00 mode from MMT. A different mechanism is needed to correct this (ASC control to MMT3).
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PART II:
Modeling LIGO’s Input Mode Cleaner (MC)
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Objectives
1. Create a complete, dynamic model of LIGO’s input mode cleaner.
2. Incorporate this model into SimLIGO and study the how the mode cleaner’s performance affects LIGO’s sensitivity.
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LIGO’s Mode Cleaner:Length Sensing Servo
From PSL
Resonance: L = (n+½ )*λ
To Interferometer
Pockels Cells
Pound-Drever-HallLocking Mechanism
PhotodetectorDemod
error α delLength
Coils
Mags
Push or PullMC2 (Z)
33.289 MHz
Digital filters
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LIGO’s Mode Cleaner:Alignment/Wavefront Sensing Servo
From PSL
33.289 MHz
124
3WFS1
WFS2
+_
+_
124
3
+_
+_
WFS1 PIT α MC2pit
WFS1 Yaw α MC3yaw –MC1yaw
WFS2 PITα MC3pit +MC1pit
WFS2 YAW α MC2yaw
MC3ASCPITMC3ASCYAW
MC2ASCPITMC2ASCYAW
MC1ASCPITMC1ASCYAW
P = 10 HZ 0.01 HZ 0.01 HZZ = .5 HZ 0 HZ
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Modeling LIGO’s Mode Cleaner
LSC
ASC
Realistic Seismic Motion
Suspensions CavityLaser
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GeophoneHAM stack box
X in
Y in
Table u
Table v
MMT3(-0.8, 0.6)
(0, 0)MC3(0.75, -0.05)
MC1(0.75, -0.25)
SM(0.75, 0.45)
MMT1(0.1, 0.4)
Table’s Motion@ center of massTable yaw
Mirror SusPt u
MirrorSusPt v
MirrorSusPt yaw
Calculation of SusPt Motion
c.f. LSC Aug ‘04
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Results:MC Transmitted Power
ASC OFF ASC ON
1.0% 0.1%±1.0% ±0.1%
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Results:Fourier of Transmitted Power (TEM00)
ASC OFF ASC ON
FULL
After 5secs
2Hz
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Results:MC Transmitted Beam Pointing
ASC OFF ASC ON
Pitch = 10*Yaw ASCon = (1/3)ASCoff
θbeam = 208 urad
2% of θbeam
0.2% of θbeam 0.7% of θbeam
7% of θbeam Pitch
Yaw
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Findings
ASC OFF ASC ON
% Fluctuation in TEM00
~1.0% ~0.1%
Beam Pointing Angle
(max)
Pitch: 15 rad
Yaw: 1.5 rad
Pitch: 4 rad
Yaw: 0.5 rad
Fourier Spectrum High Low-Frequency Component
Low-Frequency Suppressed
Time Series Low-Frequency oscillation
Noticeable 2 Hz oscillation
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Conclusion (Part II)
Alignment Sensing serves a vital role in the Mode Cleaner’s stability. This servo reduces the beam pointing angle and helps to maximize the power coupled into the cavity, resulting in increased power in the laser’s TEM00 mode.
Model Complete
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Future Work:
Now that the Mode Cleaner has been completely modeled, I have begun to incorporate this box in SimLIGO. We will study the affect of mode cleaner on the power coupled into the cavities as well as its affect on the differential arm signal.
Update current model to study Advanced LIGO’s input mode cleaner
Study the effect of the input beam’s fluctuations when all of the core optics receive seismic noise
Activate the arm cavities’ ASC to act upon MMT3, stabilize the input beam to the RM.
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Thanks SURF!