TCS and IFO Properties
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Transcript of TCS and IFO Properties
TCS and IFO Properties
Dave Ottaway
For a lot of people !!!!!!LIGO Lab
Kavli Institute for Astrophysics and Space Research,
Massachusetts Institute of Technology
March ’05 LSC Meeting 2
Outline of Talk
The Questions Thermal Issues in LIGO 1 Optic The TCS system The static spatial offsets in the IFO The excess absorption in H1 Optics Conclusions
March ’05 LSC Meeting 3
Steady state effect of absorption on the optics
0.02 0.04 0.06 0.08 0.1 0.120
0.02
0.04
0.06
0.08
0.1
radius (m)
de
pth
(m
)
Temnperature Profile for 1 Watt Coating Absorbtion
1
2
3
4
5
6
0.02 0.04 0.06 0.08 0.1 0.120
0.02
0.04
0.06
0.08
0.1
radius (m)
de
pth
(m
)
Temnperature Profile for 1 Watt Substrate Absorbtion
1
1.5
2
2.5
OPDcoating/OPDsubstrate = 2.9 for surface reflection
OPDcoating/OPDsubstrate = 0.95 for optics transmission
Model does not include deformative effects of the coatings
0 0.02 0.04 0.06 0.08 0.1 0.12
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
radius (m)
OP
D (
um
)
Optical Path Difference in Transmission for 1 W absorption
CoatingSubstrate
0 0.02 0.04 0.06 0.08 0.1 0.12-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
radius (m)
OP
D (
um
)
Surface Distortion in for 1 W absorption
CoatingSubstrate
March ’05 LSC Meeting 4
Effect of Heating Optics
Effects are biggest when inner optics are heated ie Beamsplitter and Input Test Masses
Has minimal effect on Carrier power (stabilized by the arms)
Common heating (equal heating of the ITMs effects) sideband build-up and mode shape in the power recycling cavity
Differential heating effects AS_I level and phase noise coupling
March ’05 LSC Meeting 5
Initial LIGO TCS Concept
CO2 Laser
?Over-heat mask Under-heat mask Inhomogeneous mask
ZnSe Viewport
Over-heat pattern
Under-heat pattern
Raw Heating pattern
March ’05 LSC Meeting 6
Effect of TCS on Optics
0 0.02 0.04 0.06 0.08 0.1 0.12-0.1
-0.05
0
0.05
0.1
radial direction (m)
OP
D (
um
)
Correction Profile vs Rinner
0.040.050.060.07
• Initial TCS used binary masks
• Very successful for factor of 3 overheat
•Beyond this more improved masks are needed – Sub resolution structure
March ’05 LSC Meeting 7
Time Constants of TCS Heating
0 5000 10000 150000
0.5
1
1.5
2
2.5
3
3.5
4x 10
-5 Lensing vs Constant Annulus Heating
Time (s)
Th
erm
al L
en
s P
ow
er
(arb
. un
its)
VerticalHorizontal
0 1000 2000 3000 4000-6
-5
-4
-3
-2
-1
0x 10
-4 ITMX Lensing vs time for IFO cooldown
Time (s)
The
rmal
Len
s P
ower
(dio
ptre
/Wat
t on
MC
)
VerticalHorizontal
•Annulus heating has complicated time dependence
•Heat flow into the center
March ’05 LSC Meeting 8
Time Constant in Annulus Heating
•Reduction of TCS Power with time is due to heat flowing into the center of the optic which reduces TCS efficiency
•See talk by Stefan
March ’05 LSC Meeting 9
Effect on TCS Laser Noise on IFO performance
Predicted actuation agrees within 10% (ie experimental error)
Noise for 3nV circuit and 10 Watts Annulus heating
Thermal expansion of HR surface is the dominant noise term
102
103
104
10-19
10-18
10-17
Predicted Displacement Noise Due to TCS
Frequency (Hz)
Dis
pla
cem
en
t (m
/rtH
z)
SRDTCS Noise
March ’05 LSC Meeting 10
Overall TCS Performance
H1 achieves sideband build-up at ~ 2 watts
Cannot lock reliably without TCS at ~ 4 Watts input
Reduces oscillator phase noise sensitivity, which is dominant at higher frequencies
Increases sideband to maximum Does not have enough power to
correct H1 at 4 Watts input H1 show significant 1.064 um
absorption A nice servo for TCS (See
Stefan’s commissioning talk)
• Green curve (Without differential TCS)•Blue curve (With differential TCS)
March ’05 LSC Meeting 11
Livingston TCS Performance
Is not plagued by the same thermal issues as H1. No sign of 1.064 um heating NSPOB level increased from 150 – 330 Sideband power to dark port increase as NSPOB Optical Gains Increase (Not quite what you would expect)
» Darm ~ NSPOB0.8
» POB_I , POB_Q ~ NSPOB2
» Refl gain increases Results confirmed by FFT modeling Reduces phase noise sensitivity by 10 DC AS_I Level Reduced by a factor of 3 System becomes unstable when TCS reduces AS_I to zero
» This is not understood TCS runs open loop, no servo used Currently operating at 6 Watts of 1.064 micron input Summary provided by Valery Frolov
March ’05 LSC Meeting 12
Optimum power to correct static curvature errors
IFO ITMX ITMY
LHO 4K 35 52 27 60 82 60
LHO 2K 0 57 17 110
LLO 4K 22 53 39 83
• Experimental Data (Blue), Simple Curvature Model (Black) and Full FFT (Green)• Model results by Hiro, additional power required for BS ROC• Measurements assume a 15% loss from the calibration point to the power
March ’05 LSC Meeting 13
Optical Absorption in the IFOs
IFOs are originally designed as a point designed with 1.06um absorption needed to get to optimum operating point» 12mW in coating and 16 mW in substrate for 6 Watt input
» Substrate absorption ~ 4 ppm/cm, Coating absorption ~ 0.5 ppm
» Numbers from Ryan Lawrence’s PhD Thesis
H1 gets to the optimum operating point with ~ 2 Watts of power
L1 shows expected heating H2 show negligible 1.064 um heating
March ’05 LSC Meeting 14
Measurements to quantify absorption in H1
Significant power potentially absorbed in various optics
TCS servo to optimize heating power (Stefan B)
» Determine reduction in central heating required at each power level
» Sensitive to power absorbed in BS, ITM coatings and substrate
» Measures optimal absorption
G factor measurements (Rick S, Malik, Bill K and Keita)
» See talk by Rick Savage
Spot size measurements (Dave O and Joe B)
March ’05 LSC Meeting 15
Spot Size Measurement
AS Port Optics
Camera Spiricon Software
TCS Beam
RM
ITMY
ITMX
0 2 4 6 8 10 12 14 16 1865
70
75
80
85
90
95
Time (Minutes)
Wai
st S
ize
(arb
.)
Spot Size vs Cooling Time
TCS (Sag)
Fit
TCS X (Tan)
Fit
IFO Heat (Sag)
Fit
IFO Heat (Tan)
Fit
•Auxiliary have since been done
•Calibrated using TCS
March ’05 LSC Meeting 16
What are these measurements sensitive to ???
* Depends on exact location of heating
Mirror ITMX ITMY ETMX ETMY BS
Measurement No Coating/Substrate C S C S C C S,C
1 Xarm TCS 1 1.05 1
2 Yarm TCS 1 1.05
3 Xarm G factor 1 0.34 0.52
4 Yarm G factor 1 0.34 0.52
5 POB Spot Size 1*
6 POX Spot Size 1 1.05 0.25
7 POY Spot Size 1 1.05
March ’05 LSC Meeting 17
The Results so far
TCS optimal heating» 16 +/- 3 mW per W (Ypath), 43 +/-8 mW per W (Xpath)
G factor changes» 24 +/- 3 mW per W (Xarm), 15 +/- 5mW per W (Yarm)
Spot size changes » 12.6 +/- 1.6 mW per W (ITMY), 34mW +/- 5mW per W (ITMX)
H1 ITMX absorbs at the level of about 26 ppm Heating in the bulk cannot be eliminated New ITMX is being prepared See T050074-00-R
March ’05 LSC Meeting 18
Conclusions
A considerable amount of progress has on determining the spatial properties of the IFO and compensating errors using the TCS system
Significant amount of power is absorbed in either the H1 ITMX and ITMY is not pristine either
If this is not corrected ~ 10 Watts of TCS correction will be required to reach the SRD
New higher power TCS laser has been installed on the ITMX to enable the delay of the ITMX swap until after S5
March ’05 LSC Meeting 19
Time Constant in Annulus Heating
•Reduction of TCS Power with time is due to heat flowing into the center of the optic which reduces TCS efficiency
•See talk by Stefan