Transcript Diapositiva 1 - Istituto Nazionale di Fisica Nucleare

TCS update
INFN Roma Tor Vergata
Thermal Lensing Effects in Advanced Virgo
• Thermal compensation for Advanced Virgo, must take into
account the much greater circulating laser power (~800kW)
• In Advanced Virgo, thermal effects will create distortions both
in the recycling and in the Fabry-Perot cavity:
– Wavefront distortion in the PRC
– HR surface elastic deformation
•The cavity becomes less concentric,
and the spot sizes at the mirrors will
shrink (increase of thermal noise and
reduction of arm cavity coupling to the
input beam)
•Necessity to control the radii of
curvature of all test masses, TCS will
have to act on both ITM and ETM.
From S.Chelkowski presentation at 1.7.08
beweekly meeting
Advanced Virgo Meeting - 16.07.08
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Advanced LIGO and Advanced Virgo share the same thermal issues. A
possible TC System has already been proposed in the LIGO Collaboration
Advanced LIGO TCS scheme
Compensation plates will correct
thermal effects in the PRC
Shielded heating rings will
compensate HR surface
deformations
Hartmann sensors will be used to
monitor TM and CP phase profile
In the case of Advanced Virgo,
The positioning of CPs in the PRC
is a delicate issue due to its strong
impact with the suspension
systems
Red dots: shielded heating ring
Green rays: CO2 heating beams
Blue rays: sensing beams
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
In the simulation we used the following parameters:
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125W of input ITF power, beam radius on TM = 6 cm
FP cavity Finesse=885
gain of the SRC=23.5
absorptions of the coating and substrate respectively 0.5ppm
and 2ppm/cm
Total absorbed YAG power ~0.5W
Test Mass diameter: 350 mm
Test Mass thickness: 200 mm
Test Mass ROC (cold): 1530 m
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM
- Thermoelastic deformation
Thermo-elastic deformation of the HR surface
Change in the ROC

Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM
- Lensing effect (thermooptic 95% + thermoelastic 5%)
Optical path length increase in the substrate.
The focal length of the equivalent lens is 4.5 km
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Is it possible to correct both effects acting with a CO2 beam on the HR
face of the ITM?
-
heating profile due to AXICON
internal radius = 6 cm
external radius = 16 cm
} Not optimized
Optical path length for different CO2 powers
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Is it possible to correct both effect acting with a CO2 beam on the HR
face of the ITM?
-
heating profile due to AXICON
internal radius = 6 cm
external radius = 16 cm
Temperature map for 9.7W of CO2
} Not optimized
HR face displacement for 9.7W of CO2
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Is it possible to correct both effect acting with a CO2 beam on the HR
face of the ITM?
-
heating profile due to AXICON
internal radius = 6 cm
external radius = 16 cm
} Not optimized
ROC for different CO2 powers
ROC=1567 m
ROC=1556 m
ROC=1538 m
ROC=1530 m
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Since the ROC increases when heating the HR
face, we tried acting with a CO2 beam on the AR
face of the ITM. Same profile as HR heating.
The lensing effect is corrected at (almost) the same level
as when acting on the HR face.
What about the radius of curvature?
ROC for different CO2 powers
ROC=1518 m
ROC=1538 m
ROC=1530 m
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
From the simulations it follows:
•Front heating increases
ROC (~3.1 m·W)
•Back heating decreases ROC (~2 m·W)
Need to find the correct balance between front and back heating
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
CO2 heating on both faces
Starting from these evaluations we
heated the TM on both faces, with the
same profile, but different powers: 2.5
W on the HR face, 7.5 W on the AR
face.
Effect on the ROC
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
CO2 heating on both faces
Effect on the OPL
Temperature map
OPL
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TCS Noise Coupling Mechanisms
• Thermoelastic (TE)- fluctuations in locally
deposited heat cause fluctuations in local
thermal expansion
• Thermorefractive (TR)- fluctuations in
locally deposited heat cause fluctuations
in local refractive index
• Flexure (F)- fluctuations in locally
deposited heat cause fluctuations in
global shape of optic
AdvancedLIGO
VirgoLaboratory
Meeting - 16.07.08
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Flexure Noise- A Simple Model
CM line
A very skinny mirror with
‘annular’ heating
heating
slat mirror
probe beam
heating
The probe beam sees the mirror
move at the center due to
wiggling far from center
Advanced Virgo Meeting - 16.07.08
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Ad Virgo TCS noise
20
Zemax profile
Fit
Evaluation of the flexural noise
15
Heating profile from Zemax fitted with:
2r 2
64 10 5  r 2 2 2 2  w12
H(r) 
w2  r  e

W/m2
2 4
w1 w 2
w1=0.099 and w2=0.0048

10
5
0
0
0.05
0.1
0.15
0.2
This profile has been fed to a structural simulation in COMSOL to calculate the
displacement of the HR face wrt the CM
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Ad Virgo TCS noise
21
1 10
In case the CO2 is applied on the HR face,
to have TCS noise 10 times smaller than
AdVirgo sensitivity @ 50 Hz RIN must be
5·10-9 1/Hz
TCS noise total
FL noise
TR + TE noise
Rad pressure noise
AdVirgo sensitivity
22
1 10
23
1 10
24
Flat RIN over the entire frequency band
No relevant change with TM 30 cm thick
1 10
25
1 10
26
1 10
10
100
3
1 10
4
1 10
A cross check between the model with experimental data (Edwige from TCS
commissioning) and analytical calculations (S. Ballmer) is in progress
In case of heating on both sides of the TM, the noise model must be reviewed to take
into account possible cancellation mechanisms.
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
We started to investigate the behavior of heating ring, from a question done by
Andreas:
An interesting idea could be to optimize the ROC for a normal TEM00 modes then at a later stage use the TCS to change the ROC in
order to adapt the cavities for higher order modes. Do you have any idea of how much static change we could get, say, from a ring heater
without creating other problems? I am thinking of changing a ROC of maybe 1530m to 1600m or 1630m or so.
Geometry description: axisymmetric model
Model components: mirror with a cold ROC = 1530 m + ring heater placed in front of
the HR face of the mirror at a distance of 5.5 cm.
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
Temperature distribution in the mirror
(cold mirror at T= 295 K)
Displacement of the HR face
160 W delivered by the Heating ring. Temperature of the HR = 530 K
Advanced Virgo Meeting - 16.07.08
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Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
Effect on the ROC
160 W delivered by the Heating ring. Temperature of the HR = 530 K
Detailed calculations not yet performed (need to model the LG33 effect).
Thermal lensing is probably overcorrected! This is possible only on ETM
Advanced Virgo Meeting - 16.07.08
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Next steps in simulations
• Check of the noise model
• Investigate the possibility to relax the RIN requirements with
both faces heating
• Possibility to replace the CO2 beam on the back with a heating
ring
• Evaluate the noise introduced by the heating ring
• Study the case of HOLM:
– possibility to change statically the ROC to optimize it for the HOLM
– determine the TCS requirements
• Determine the requirements of a possible CP
• Study interaction of the TCS with nearby optics and hardware
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