L ocal S uspension P oint I nterferometer for CLIO

Local Suspension Point Interferometer for CLIO

University of Tokyo, ICRRA, AISTB

Takanori Saito, Souichi TeladaB, Takashi UchiyamaA,

Shinji MiyokiA, Osamu MiykawaA, Masatake OhashiA

and CLIO Collaborators

1GWADW at Hearton Hotel Kyoto2010/05/17

1. Motivation2. LSPI

CLIO suspension system Tandem Interferometer

3. LSPI Installation in CLIO CLIO in Kamioka mine Experimental setup

4. Experiment and result5. Summary

GWADW at Hearton Hotel Kyoto 22010/05/17

Outline

1. Motivation


Experiences from CLIO experimentLocking FP cavity is difficult in cryogenic temperature.

No damping resonant peaks of CLIO suspension effectively.Problems on present eddy current damping system

Damping force strongly depends on temperature. Because the damping force depends on resistance of a mass. The resistance is drastically changed from the room temperature to the

cryogenic temperature.

Needed a new damping system.Solution: active damping system

Damping resonant peaks of CLIO suspension. No large magnets. Adjustable damping force and frequency range. Low noise sensor if using interferometer.

2. Current Suspension system


6 stages suspension system.Upper 3 stages in room temperature part Lower 3 stages in cryogenic temperature part

Eddy current damping is being applied to the cryo-base by some magnets on damping stage.

Existing eddy current damping system will be replaced by active damping system in future.

Sensing and actuation point: cryo-base (not the test mass) Local Suspension Point

Main FP cavity will be used as a sensor to see the damping effect.

We call it Local Suspension Point Interferometer.

Cryo-Base

Test Mass

Cryogenic Temperature part

Room Temperature part

CLIO Suspension

3-stages vibration isolation system

Damping Stage

Upper Mass

Cryostat


PD

PBS1

PBS2

QWP1

QWP3

HWP2

PBS3

HWP1

PD

Electrical objects (actuators, PD, Laser source) don’t work in cryogenic temperature.

They are placed in room temp. part.To align the optics in cryogenic

temperature part is difficult. Not using simple Michelson

interferometer. Aligned from the room temperature

part remotely.

Avoid reconstructing the vacuum tank of CLIO.

Room arms

Cryogenicarms

Mirror1

Mirror2

Mirror4

QWP2

QWP4

S-wave

P-wave

Laser

2. Polarized Tandem InterferometerRoom

Temperature part


Mirror3


PD

PBS1

PBS2

QWP1

QWP3

HWP2

PBS3

HWP1

PD

Tandem interferometer Compensating optical path

length difference at cryogenic part by room temperature part.

Compact structure in the cryogenic temperature part.

Polarized interferometer. High contrast interferometer

Sensing pendulum motion of the cryo-base.

Room arms

Cryogenicarms

Mirror1

Mirror2

Mirror4

QWP2

QWP4

S-wave

P-wave

Laser

2. Polarized Tandem InterferometerRoom

Temperature part


Mirror3

History of LSPI experiment2008: Table-top experiment at Kashiwa Lab..2009-2010: First LSPI Installation in CLIO. Installation of optics in perpendicular arm end

suspension. Control test with existing eddy current damping Using aLIGO type digital system as servo Verified damping effect by LSPI.

Future Work Control test without the eddy current damping. Cryogenic test. Installation of second LSPI in other suspensions. Cooling all the test mass with LSPI systems.

3. LSPI Installation in CLIO


Per-arm End Suspension

CLIO Overview


3. Schematic of LSPI for CLIO

Two interferometers are installed for 2 DOFs

damping pendulum and yaw motion no big motion on pitch.

Two laser sources.Two corner cube mirrors (CCM)

are attached on the cryo-base.

Cryo-Base

UpperMass

TestMass

Cryogenicarms

PD

Laser Room arms

Essentially sensingthis length

Overview

Cryo-BaseUpperMass

TestMass

Cryogenicarms

PD

Laser

Essentially sensingthis length

Room arms


Overview

3. Schematic of LSPI for CLIO

Feedback points for length control.1. Cryo-base Damping the suspension system. Control in low frequency range (< 2Hz)

2. Active mirrors Control in high frequency range (2 ~ 20Hz)

Feedback the high frequency component to Active mirrorsavoids spoiling current CLIO sensitivity

Activemirrors

3. LSPI Setup (Room Temp.)


M3PBS3

PD

Active mirrors

Laser tank

Wave length: 633nmPower: 0.9mW

Into cryo.temp. part

From cryo.temp. part

PBS

Fixedmirror

3. LSPI Setup (Cryo. Temp.)


Reference mass

PBSQWP

Mirror

Coil-magnet actuators

From roomtemp. partInto room

temp. part

CCM

Mirror

115

Pendulum Second Mode(1.18Hz)

4. Damping test of LSPI

122010/05/17

Frequency [Hz]

Arb

itrar

y U

nit

13.5

Pendulum First Mode(0.48Hz)

GWADW at Hearton Hotel Kyoto

Transfer function of CLIO suspension

Measurement: 1. Excite test mass of main

100m FP cavity with/without LSPI lock during FP cavity locked.

2. Measure transfer function from excitation point to main mirror motion shown at the feedback signal of FP cavity control.

CLIO sensitivity with LSPI


We can expect that a suitable filter to the cryo-base loop can avoid to spoil the CLIO best sensitivity.

Frequency [Hz]

Dis

plac

emen

t [m

/rtH

z]

Two loops control. Cryo-base and active mirrors.

Add the 6Hz LPF only to cryo-base loop.

Improving CLIO sensitivity.

LSPI (Local Suspension Point Interferometer) is Local control system that has two polarized tandem interferometers

to damp the fluctuation of cryo-base. Installed to 1 of 4 main suspensions.

We succeeded in damping the resonant frequency of CLIO pendulum (0.48Hz, 1.18Hz) using LSPI.

Feeding back low frequency signal to cryo-base and high frequency signal to active mirror successfully avoided spoiling CLIO sensitivity around 20Hz.


6. Summary

L ocal S uspension P oint I nterferometer for CLIO

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