Institute for Cosmic Ray Research Univ. of Tokyo

Development of an RSE Interferometer Using the Third Harmonic Demodulation

LIGO-G010322-00-Z

Osamu Miyakawa,Kentaro Somiya A,Gerhard Heinzel B,Seiji Kawamura C

ICRR Univ. of Tokyo, Dept. of Advanced Materials Science, Univ. of Tokyo A ,

Max-Planck-Institut fuer Gravitationsphysik B ,NAO C

Aug. 2001 @ LSC

Institute for Cosmic Ray Research Univ. of Tokyo

Suspended-mass RSElocked for the first time

in the world

using single modulationby Third Harmonic Demodulation

Institute for Cosmic Ray Research Univ. of Tokyo

Purpose of our experiment Signal sensing for SEC using Third Harmonic

Demodulaiton Experiment Summary and next plan

Contents

Institute for Cosmic Ray Research Univ. of Tokyo

Purpose of our RSE experiment

・ Different from real interferometer・ Only low finesse available・ Complicated (Transmission of MC, Control scheme)

Other table top experiments Feature

・ Fixed mirror in the air

・ Multi modulations

Objectives/Scope・ To establish the control scheme using single modulation・ Suspended mirror・ High finesse cavity in vacuum chamber

Institute for Cosmic Ray Research Univ. of Tokyo

Most difficult point of RSE lockingthe extraction of

a Signal Extraction Cavity(SEC) signal(ls).

Mixture of L+ and L- signalto ls signal is quite large.

Need to improve the signal ratio of ls–multi modulation–establish a new sensing scheme using single modulation

Institute for Cosmic Ray Research Univ. of Tokyo

Application of 3rd order harmonic demodulation

1st order demod.

(Sb2,-2)(Sb1,-1) (Sb2,-2)(Sb1,-1) s

(Sb1,-1)(Ca) - ,

DC

DC

DC

lLL

Sb1Sb-1Sb2Sb-2

Sb3Sb-3

Ca

L+, L- ls

sum

3rd order demod.Ca

Sb2Sb-2Sb3Sb-3

Sb-1 Sb1

L+, L- ls

(Sb2,-2)1,-)-(Sb 2,2)-(Sb(Sb1,-1) s

(Sb3,-3)(Ca) - ,

DC

DC

DC

l

LLzerosum

Institute for Cosmic Ray Research Univ. of Tokyo

Dark condition of 3rd order sideband

Asymmetry in Michelson 3rd order sidebands vanish at t

he anti symmetric port

I17.25MH

EOM I solator

Asymmetry( ～ 3m)

51.75MHz

x3

FrequencyTripler

17 ． 25MHz

Institute for Cosmic Ray Research Univ. of Tokyo

106

104

102

100

10- 2

10- 4

L- /

ls

- 40 - 20 0 20 40

Demod. phase [degree]

1st order demod.3rd order demod.

Signal ratio

The depth of improvement is depend on the asymmetry length.We can adjust the modulation frequency instead of asymmetry length to satisfy the condition.

Signal ratio of L- and lswith 1st and 3rd order demodulation If the demodulation phase is

exactly zero, L- is zero in both 1st and 3rd demodulation case, but in non zero demodulation phase case, 3rd demodulation has good signal ratio.

Institute for Cosmic Ray Research Univ. of Tokyo

RSE experimental setup・ FM,EM,BS,SEM are suspended as single loop pendulum. ・ 4m two arm cavities, finesse:1000(vacuum) or 300(air)・ 8.75m SEC, RSEM=0.6

・ Big (3m) asymmetry・ Mode matching is compensated by two lenses.

Institute for Cosmic Ray Research Univ. of Tokyo

Large vacuum chamber

Small vacuum chamber 3m Pipe

Opticalbench

Detectorbench

Experimental setup of RSE

←To smallchamber FM BS

lense

FM lense

Institute for Cosmic Ray Research Univ. of Tokyo

Small Suspension System (SSS)

Dampingmagnets

Mirror

4 magnet-coilactuators

•1 inch mirror is suspended by single-loop wire.

•Mirror position and orientations are controlled by 4 coil-magnet actuators.

•Motion of the mirror at resonant frequency is efficiently damped by the eddy-current damping.

Institute for Cosmic Ray Research Univ. of Tokyo

・ SEC error signal is extracted by Third Harmonic Demodulation at Anti Symmetric port.・ Two FP arm cavities are locked by picked-off light independently.・ Frequency is stabilized by error signal of primary arm cavity.・ Lock time is over 10 minutes.

RSE control topology using THD

・ not vacuum・ without Power Recycling・ not detuned

51.75MHz

Institute for Cosmic Ray Research Univ. of Tokyo

Lock acquisition of RSELock

Institute for Cosmic Ray Research Univ. of Tokyo

Locking selection of SR/RSEunlock Power at

dark port

Error sig. of SEC from3rd demod. at dark port

RSE lockSR lock

SR lock point

RSE lock point

Institute for Cosmic Ray Research Univ. of Tokyo

Measurement of cavity Transfer Function

DC) ( -)Gain( Optical

T.F. PendulumV1V2

L

・ Shaking L- to see the cavity response

Institute for Cosmic Ray Research Univ. of Tokyo

Transfer function

0.001

0.01

0.1

T.F.

1022 4 6 8

1032 4 6 8

1042

Frequency[Hz]

SRFPMIRSE

Transfer Function of L- with Pendulum

2 f

resonance ofpendulum

SR : upper than FPMIRSE : lower than FPMI

Institute for Cosmic Ray Research Univ. of Tokyo

• Difference between transfer function of SR and RSE at DC is 7dB.

0.1

2

4

68

1

2

4

68

10

T.F.

1022 4 6 8

1032 4 6 8

1042

Frequency[Hz]

SR/FPMISR/FPMI(cal.)RSE/FPMIRSE/FPMI(cal.)SR/RSESR/RSE(cal.)

Relative Transfer Function

Institute for Cosmic Ray Research Univ. of Tokyo

Conclusion– We locked suspended-mass Resonant Sideband

Extraction with one modulation and by Third Harmonic Demodulation.

– We confirmed the RSE and SR locking by comparing the response of the interferometer for both configurations.

Next plan– vacuum– measurement of T.F. with wide band including pole– L+ L- control– detuned RSE– Power Recycling