LIGO-G080428-00-L

LOS AbsorptionPresentation for TCS Group

Rupal S. AminTuesday, August 26, 2008

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Outline

• Motivation• Theory• Procedure• Data• Result

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Motivation

• Question:

• 1) What do we care about the absorption of the large optics?

• 2) What is the absorption value?

• Answer: Silica mirrors inside IFO unfortunately absorb resonant laser power.

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Motivation

• Ans (con’t): Mirrors expand due to temperature changes. Depending on absorption coefficient, mirrors may distort beyond or below design optimum.

Cold Hot

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Motivation

• Measuring absorption (especially the ITMS) allows TCS team to build effective absorption models (Mathematica, Matlab, Finesse, SIS)

• Correct setup scheme for Enhanced TCS. • So…We need the absorption values of the

large Fabry-Perot optics.

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Theory

• Crude theory– Mirrors have body modes

• Finite temperature Brownian motion

– Frequencies are thermally dependent • Due to Young’s modulus having a Y(T).

– Track body mode frequency evolutions due to DT– Df yields power absorption

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Theory

• Crude theory

• Better theory

• We need f and ∆f to determine α*

T

KJ

P

Kf

f abs

7390

1105.7 5

0

t s

tt

s

etT

Kt

f

f

17000'

105.10 17000

)'(5

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Procedure

• Power Cycle IFO during fully locked state.– Do this over several hours

• Save data from fast ASQ sample channels and temperature sensors.

• Download GBs of data from LDAS and analyze.

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ProcedurePwr

t

0 50 100 150 200 250 300-800

-600

-400

-200

0

200

400

600

Time (s)

AS

Q F

AS

T (

cts

)

0 1 2 3 4 5 6 7 8 9 1010

-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

Demod Freq from 9330 Hz

ITMY body mode near 9330 Hz

df/f

4 W

1 W

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Data

• Lock data from 899867714 s

• Thermal data: Mirror modes are history dependent

8.9982 8.9984 8.9986 8.9988 8.999 8.9992 8.9994 8.9996

x 108

293.06

293.08

293.1

293.12

293.14

293.16

293.18

293.2

293.22

293.24July 12, 2008 data: Temperature data from BSC 3

Tem

p (C

)

8.9985 8.9986 8.9987 8.9988 8.9989 8.999 8.9991 8.9992 8.9993 8.9994 8.9995

x 108

0

0.5

1

1.5

2

2.5x 10

4

QP

Dx

tran

s (c

ts)

GPS (x)

QPDx Transmission Data July 12, 2008

0 50 100 150 200 250 300-800

-600

-400

-200

0

200

400

600

Time (s)

AS

Q F

AS

T (

cts

)

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Thermal Resistances and Sources

•BSC and contents slow LVEA to ITM interaction time.

•Beam tubes: heat source but negligible

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Thermal Resistance

• Simulation of TM interaction with BSC. Small perturbations lead to simulation problems.

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Analysis using raw data

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Raw Data (noisy)

8.9985 8.9986 8.9987 8.9988 8.9989 8.999 8.9991 8.9992 8.9993 8.9994 8.9995

x 108

293.05

293.1

293.15

293.2

293.25July 12, 2008 data: Measured Frequency Shift of ITMy with a time shift

Tem

p (C

)

8.9985 8.9986 8.9987 8.9988 8.9989 8.999 8.9991 8.9992 8.9993 8.9994 8.9995

x 108

9325.3

9325.35

9325.4

9325.45

Mea

s. F

req.

(H

z)

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Fitting Data

G

Peak = (x0 , Amplitude)

DC based on noise average

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Analysis using fitted data

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Analysis

• ∆f/f for ITMy

8.9985 8.9986 8.9987 8.9988 8.9989 8.999 8.9991 8.9992 8.9993 8.9994 8.9995

x 108

101.5e-005

101.6e-005

101.7e-005

Mea

s. F

req.

(H

z)

delta f / f

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Results

• Total uncorrected slope = 1.3(3)e-6+/-1.3e-6 Hz/s

• Uncorrected for high power = 4.(43)e-7+/- 3. e-7 Hz/s

• Crudely Corrected slope = ?• Refined df/f = Need to do

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Ambient temperature f-drift

• Crude shift due to temperature fluctuations

8.9985 8.9986 8.9987 8.9988 8.9989 8.999 8.9991 8.9992 8.9993 8.9994 8.9995

x 108

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

GPS (s)

delta

f/f

delta f due to delta T from 9.325 kHz

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Questions?

• 1) What is your purpose?• 2) What is your favourite color?