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Locking tests with TCS

WG1 at Birmingham

July, 10th-11th 2008

Enrico Campagna

on the behalf of the Locking/TCS group

INFN Sez. FirenzeINFN Sez. Firenze Universita` di UrbinoUniversita` di Urbino

European Gravitational ObservatoryEuropean Gravitational Observatory

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SummarySummaryA description of all the tests is in EGO working area under Virgo/locking A description of all the tests is in EGO working area under Virgo/locking

Activities Activities TCS TCS Thermal compensation system in VirgoThermal compensation system in Virgo

Why we need itWhy we need it An overviewAn overview

TestsTests Step 12Step 12

10 mW10 mW Higher powersHigher powers Etalon effect, Newton ringsEtalon effect, Newton rings Trying to balance the SBs Trying to balance the SBs

with locking/alignment signalswith locking/alignment signals with input powerwith input power

Step 8Step 8 1.3 W and up to 4.4 W1.3 W and up to 4.4 W Scanning OMC temperatureScanning OMC temperature

Lock acquisitionLock acquisition 700 mW from the beginning700 mW from the beginning Various power form step 6Various power form step 6 Investigation of 11 Hz loop instabilitiesInvestigation of 11 Hz loop instabilities

Single free swinging cavitySingle free swinging cavity Changing TCS annulus shapeChanging TCS annulus shape

FutureFuture ConclusionsConclusions

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TCS in Virgo: why we TCS in Virgo: why we need itneed it

Absorbed laser power in the input opticsAbsorbed laser power in the input optics 14 ppm in the WI14 ppm in the WI 5 ppm in the NI5 ppm in the NI

Evident effect during the lock acquisitionEvident effect during the lock acquisition After reaching the DF we have to wait 10-15 min for the After reaching the DF we have to wait 10-15 min for the

ITF to thermalizeITF to thermalize Big transients on sidebands powers (great asymmetry)Big transients on sidebands powers (great asymmetry)

The cleaning with first contact polymer had no effectThe cleaning with first contact polymer had no effect The transient remained pretty much the sameThe transient remained pretty much the same Slight increase of mean SB powerSlight increase of mean SB power

TCS shouldTCS should Give the optics a constant time behavior Give the optics a constant time behavior

make the locking signal more stationarymake the locking signal more stationary make the lock acquisition fastermake the lock acquisition faster

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TCS in Virgo: an TCS in Virgo: an overviewoverview

L5

2" Hot mirrorL4

AXICON

L3

L2L1

LASY-20S

Aiming laser

1" Beam splitter

Power meter

Polarizer

Half waveplate

Beam dump

2" FM1

2" FM2

25 W CO25 W CO22 laser (only on WI) laser (only on WI) 3-4 % on power meter 3-4 % on power meter ph.diodeph.diode 2 telescopes L1-L2 and L3-L52 telescopes L1-L2 and L3-L5 Axicon: double conic lenseAxicon: double conic lense Ext. thermal cameraExt. thermal camera

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Step 12: 10 mWStep 12: 10 mW

With 10 mW we already have a strong With 10 mW we already have a strong effect on SB balancing. effect on SB balancing. NOT EXPECTED, but observed many NOT EXPECTED, but observed many

times, in subsequent tests alsotimes, in subsequent tests also Opposite to the std transientOpposite to the std transient Due to central spot? Due to central spot? Phase camera: clear effect on central area Phase camera: clear effect on central area

(movies)(movies) Towards a flatter shapeTowards a flatter shape

MORE INVESTIGATION NEEDEDMORE INVESTIGATION NEEDED

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Step 12: higher powersStep 12: higher powers Up to some hundreds mW no significant Up to some hundreds mW no significant

differencesdifferences 700 mW gives encouraging effects700 mW gives encouraging effects

SBs unbalancing as in a time-reversed std SBs unbalancing as in a time-reversed std locking acquisition transientlocking acquisition transient

Indicates a possible reduction of thermal lensingIndicates a possible reduction of thermal lensing 5 mins transient for each step in powers5 mins transient for each step in powers B5_2f_ACq is decreasing a lot even if mean SB B5_2f_ACq is decreasing a lot even if mean SB

power is increasingpower is increasing Decrease in MICH offset Decrease in MICH offset B5_DC increasing B5_DC increasing B1_DC/B1p_DC increases indicating a cleaner matching B1_DC/B1p_DC increases indicating a cleaner matching

of the SBs in the OMC of the SBs in the OMC West cavity finesse is significantly growing West cavity finesse is significantly growing

More than 1 W More than 1 W Upper SB starts going upUpper SB starts going up 11 Hz instabilities (see later)11 Hz instabilities (see later)

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Step 12: cooling down and Step 12: cooling down and etalon effect etalon effect

Switching TCS off after the testSwitching TCS off after the test The same 5-10 min fast trendsThe same 5-10 min fast trends SBs start from very low values and then slowly SBs start from very low values and then slowly

increaseincrease long trend in the optical gain of NE, WE and BSlong trend in the optical gain of NE, WE and BS

correlated quite well with the horizon correlated quite well with the horizon Clear slow trends on B5_2f_ACq and on Clear slow trends on B5_2f_ACq and on

Gc_Driving_PRCL_NE-WEGc_Driving_PRCL_NE-WE WI heating WI heating change in thickness change in thickness change in etalon change in etalon

finesse asymmetry finesse asymmetry pure common modes couple to pure common modes couple to differential differential PRCL enters differently the df PRCL enters differently the df gain beta gain beta changeschanges

but PRCL noise not limiting the sensitivitybut PRCL noise not limiting the sensitivity The same happens with B5 frequency noise The same happens with B5 frequency noise

couplingcoupling

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More on etalon: Newton More on etalon: Newton ringsrings

From mirror temperature measurement From mirror temperature measurement (resonant mode technique) (resonant mode technique) TTMM=0.3 K is =0.3 K is not enough to explain the etalon fringesnot enough to explain the etalon fringes

From FE symulation (From FE symulation (M.PunturoM.Punturo)) Locally Locally T of few degreesT of few degrees Differential radial reflectivityDifferential radial reflectivity Time dependent transmittivityTime dependent transmittivity

TCS with current configuration will never TCS with current configuration will never get rid of thermal transientget rid of thermal transient Restyle it to allow for a central spot to heat as Restyle it to allow for a central spot to heat as

the Nd:Yag laser while unlockedthe Nd:Yag laser while unlocked

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Step 12: trying to balance Step 12: trying to balance the SBs with locking and the SBs with locking and

alignment signalsalignment signals With locking signalsWith locking signals

MICH offset has little effect and fast brings B5_DC to very MICH offset has little effect and fast brings B5_DC to very low values (the std way of balancing the SBs is not low values (the std way of balancing the SBs is not working)working)

B2_3f phase and B5 phase have no effectB2_3f phase and B5 phase have no effect With TCS off, B2_8MHz phase tuned to move With TCS off, B2_8MHz phase tuned to move

B2_8MHz_ACq to 0B2_8MHz_ACq to 0 MICH offset goes to 0MICH offset goes to 0 It has no effects on B5_DC or B5_2f _ACqIt has no effects on B5_DC or B5_2f _ACq But with TCS on nothing changesBut with TCS on nothing changes

Lowering the PRCL offset Lowering the PRCL offset SBs unbalance but SBs unbalance but their power goes uptheir power goes up in another test at step 8 has no effect at all in another test at step 8 has no effect at all

Alignment signal of the input have no effects (at Alignment signal of the input have no effects (at step 8)step 8) MORE TESTS NEEDEDMORE TESTS NEEDED

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Step 12: trying to balance Step 12: trying to balance the SB with input powerthe SB with input power

Two successful tests performedTwo successful tests performed Increase TCS powerIncrease TCS power Increase up to 9.3 W IMC transmitted Increase up to 9.3 W IMC transmitted

power in order to balance the SBspower in order to balance the SBs Obvious gain in the B1 shot noiseObvious gain in the B1 shot noise

Around 15% PAround 15% PIMCIMCincrease gives a 7% shot noise increase gives a 7% shot noise reductionreduction

No particular signal worsening detectedNo particular signal worsening detected

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Moving the locking offsets Moving the locking offsets at step 12at step 12

Sensitivity comparison with TCS Sensitivity comparison with TCS off/on/unb-sboff/on/unb-sb

TCS power-noise budget TCS power-noise budget (E.Tournefier)(E.Tournefier) From noise measurementFrom noise measurement Stating a 1/f Stating a 1/f matching 596 Hz linematching 596 Hz line

Thanks to Edwige

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Step 8: up to 4.4 WStep 8: up to 4.4 W With the same configuration as during the With the same configuration as during the

transient (transient (MICH on B5_ACq and PRCL on B2_3f_ACpMICH on B5_ACq and PRCL on B2_3f_ACp)) USB reaches very low values USB reaches very low values

(SFP reconstruction fails)(SFP reconstruction fails) Looking at phase camera:Looking at phase camera:

At about 1.3 W the ITF behaves like a “cold” oneAt about 1.3 W the ITF behaves like a “cold” one Should correspond to equal input mirror RoCsShould correspond to equal input mirror RoCs

Long unlockable periodLong unlockable period Only two locking trialsOnly two locking trials Saturation of PR_zCorr signal but with different Saturation of PR_zCorr signal but with different

behhaviors: behhaviors: Step 6.5 unlock (25-30 Hz oscillation of PRCL loop)Step 6.5 unlock (25-30 Hz oscillation of PRCL loop) Step 7.5 unlock (145 Hz oscillation on all the loops)Step 7.5 unlock (145 Hz oscillation on all the loops)

Not enough to conclude anythingNot enough to conclude anything

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Step 8: scanning OMC Step 8: scanning OMC temperaturetemperature

In the normal state the In the normal state the total SB power in the df is about 27.9 mW total SB power in the df is about 27.9 mW

46% TEM0046% TEM00 54% Laguerre54% Laguerre

With 1.5 W TCS laser powerWith 1.5 W TCS laser power 53.1 mW (doubled!)53.1 mW (doubled!)

87% TEM0087% TEM00 13% Laguerre13% Laguerre

Going to 2W slightly increases the total powerGoing to 2W slightly increases the total power SBs strongly unbalanced SBs strongly unbalanced

rotating B2_3f phase (for best P/Q at PRCL 62 Hz line) rotating B2_3f phase (for best P/Q at PRCL 62 Hz line) of 12 degrees it unlocksof 12 degrees it unlocks

Possible explanation: Possible explanation: LSB has a good Gaussian shape ( LSB has a good Gaussian shape ( high recycling gain) high recycling gain) USB has almost completely a Laguerre shape ( USB has almost completely a Laguerre shape ( almost almost

no recycling gain)no recycling gain) Without the new phase camera there is no way to prove it. Without the new phase camera there is no way to prove it.

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Lock acq.: 700 mW from the Lock acq.: 700 mW from the beginningbeginning

Starting with an already heated WI mirror with 700 Starting with an already heated WI mirror with 700 mW mW B5_2f power starts from higher values at the beginning of B5_2f power starts from higher values at the beginning of

the lock acquisition and decreases slower than usual. the lock acquisition and decreases slower than usual. At the MICH/PRCL mixing now there is no powers stepAt the MICH/PRCL mixing now there is no powers step

B2_3f_ACp responds in a different way to MICH displacement B2_3f_ACp responds in a different way to MICH displacement At the MICH PRCL driving matrix reshuffling signals seem to At the MICH PRCL driving matrix reshuffling signals seem to

come back to the “normal” configurationcome back to the “normal” configuration 8MHz more or less the same as before, B2_3f is changed by the 8MHz more or less the same as before, B2_3f is changed by the

TCS TCS TCS has a clear effect on the ITF working pointTCS has a clear effect on the ITF working point

It is not clear what really happensIt is not clear what really happens Is it a good thing?Is it a good thing?

MORE TESTS NEEDED MORE TESTS NEEDED STARTING WITH LOW Nd:Yag POWERSTARTING WITH LOW Nd:Yag POWER

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Lock acquisition: with Lock acquisition: with various power from step 6various power from step 6

Modifying the lock acquisition in Modifying the lock acquisition in order to survive in the old dying order to survive in the old dying high-power statehigh-power state DARM on B1pDARM on B1p As soon as ITF in df (on B8_ACp) we As soon as ITF in df (on B8_ACp) we

switch on the TCS at various powersswitch on the TCS at various powers No evident effectsNo evident effects

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Investigation on 10-11 Hz Investigation on 10-11 Hz instabilitiesinstabilities

At step 12 “resonance” appearing on MICH and PRCL At step 12 “resonance” appearing on MICH and PRCL loopsloops

Similar instability triggered by BS-marionette Similar instability triggered by BS-marionette reallocationreallocation

Beta servo non working well around 10 Hz (different Beta servo non working well around 10 Hz (different shape from PRCL to B1)shape from PRCL to B1)

Measurements on PRCL OLTF while moving the MICH Measurements on PRCL OLTF while moving the MICH driving term to PR show something around 10 Hz driving term to PR show something around 10 Hz

Not well balanced BS marionette re-allocation?Not well balanced BS marionette re-allocation? Measure BS TFs Ma=MarioMeasure BS TFs Ma=MarioB1, RM=RMassB1, RM=RMassB1, zGc=z_GcB1, zGc=z_GcB1B1 Ma/RM gives the filter to be used for reallocation ( but fMa/RM gives the filter to be used for reallocation ( but fzz<0 )<0 ) zGc/RM actuation unbalancing to be compensated zGc/RM actuation unbalancing to be compensated TO BE IMPLEMENTEDTO BE IMPLEMENTED

= =

MICHMICH

PRCLPRCL

BSBS

PRPR

0.7070.707 00

-2.33-2.33 -1-1

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Single free swinging Single free swinging cavitycavity

We locked the two arms (step 1) and then We locked the two arms (step 1) and then We induced several unlock (up to 0.9 W TCS We induced several unlock (up to 0.9 W TCS

power)power) Look at WI free swinging cavityLook at WI free swinging cavity

estimate the elastic deformation (RoCs) of the WI HR-estimate the elastic deformation (RoCs) of the WI HR-coating surface from measuring higher order mode coating surface from measuring higher order mode (TEM02) frequency shift ((TEM02) frequency shift (R.Day/B.SwinkelsR.Day/B.Swinkels))

Main peak identificationMain peak identification Sub-peak identificationSub-peak identification Frequency shift Frequency shift

Compare the result with what is expected (0.3 % Compare the result with what is expected (0.3 % shift)shift) Slight shift detected (about 5 time less then expected)Slight shift detected (about 5 time less then expected)

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Unlockable period after Unlockable period after single cavity testssingle cavity tests

5 unlocks at step 5.55 unlocks at step 5.5 Pretty much at the moment of reaching the Pretty much at the moment of reaching the

dark fringedark fringe Similar behaviorsSimilar behaviors

Unlock due to B5_d2_ACp (SSFS) fast oscillationUnlock due to B5_d2_ACp (SSFS) fast oscillation B5_d2_ACp dirty since some seconds (except #2)B5_d2_ACp dirty since some seconds (except #2) #4 very dirty DARM#4 very dirty DARM

2 unlocks at step 6.5 (#5 and #8)2 unlocks at step 6.5 (#5 and #8) 30 Hz DARM oscillation30 Hz DARM oscillation B5_d2_ACp saturationB5_d2_ACp saturation

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Changing the TCS laser Changing the TCS laser shapeshape

Std rStd rININ=5 cm, r=5 cm, rOUTOUT=20 cm=20 cm increase of about 40% the rincrease of about 40% the rININ same laser power same laser power No visible effect on transient signalsNo visible effect on transient signals

DL3-AxiincreasedDL3-Axidecreased

Not the actual shape Not the actual shape

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ConclusionsConclusions To be understood:To be understood:

Origin of 10 mW effectOrigin of 10 mW effect if it is a physical problem on the system should ABSOLUTELY be if it is a physical problem on the system should ABSOLUTELY be

solved solved (we want to perform accurate locking test with low power)(we want to perform accurate locking test with low power)

What signal to control SB balancing (alignment…)What signal to control SB balancing (alignment…) Free swinging cavity null resultFree swinging cavity null result

To be done:To be done: Central spot TCS for avoiding Newton ringsCentral spot TCS for avoiding Newton rings Tests with low Nd:Yag powerTests with low Nd:Yag power

Phase camera 1 installation to understand the actual SB Phase camera 1 installation to understand the actual SB behaviorbehavior

New BS marionette re-allocation filter implementationNew BS marionette re-allocation filter implementation

Trying to survive in the old dying high power stateTrying to survive in the old dying high power state Tests varying the annulus shapeTests varying the annulus shape

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