Ponderomotive amplifier to reduce shot noise

GWADW @ Kyoto

May. 2010

Kentaro Somiya1 and Yanbei Chen2

Waseda Inst. for Adv. Study1 and Caltech2

High-freq sensitivity of GWD

RSE

HighFinesse

anti-reso

reso reso

SR gain could be higher if the arms were shorter.

Optical-bar regime by Braginsky and Khalili

SRM

PRM

Optical-bar regime

locked by opt spring

local-readout (high SRG)

ITM ETM

• Dual Recycling instead of PR+RSE (f<spring)• Signal enhancement at spring frequency• High power required to increase spring frequency

[Braginsky 98] [Rehbein 07]

local-readout

interpretation

Optical lever[Khalili 02][Danilishin 06]

• Reasonable power on the small mirrors• Chen-type optical lever is rather an amplifier• GW signal converts to radiation pressure in PA

interpretation

more signal less power

[Chen 03]

Ponderomotive amplifier

locked free

40kg

4km 1g

1m

Ponderomotive amplifier40kg

4km 1g

1m sig (phase)

sig (amp)

pump (amp)

RP sig (phase)

RP sig (amp)

sig (phase)

carrier (amp)

GW signal

coupled with pump

RP signal reenters

coupled with carrier• Vacuum enters from the pick-off• Optimized combination of the two outputs in the best quadrature

Ponderomotive amplifier

A

B

I1 I2

A=B=

……

I1 x … + I2 x … + …

maximize SNR

I2 x [vacuum + signal + disp-noise]GWD

Amp

Shot noiseSignal

4TcosI1(1-T)

: detune phase T: transmittance of input coupler

input coupler

If I2-term is dominant…

Signal is amplified and SNR increases

Sensitivity gain

GWD L=4km, m=40kg, I0=1kW, F=120

PA L=10cm, m=1g, I0=100W, F=6000

IC R=81%, =1.5rad

• Big reduction of shot noise up to kHz• Strong against PD losses• Power on PA might be a bit high…

PA displacement noise

• The small-mirror IFO will be noisy• The motion is suppressed by the optical spring

Sensitivity curve

• Not yet fully optimized• Good sensitivity with low power• PA noise limits the sensitivity at high freq

PBS

Single-path ponderomotive amplifier

I1 I2

GWD

Amp

vacuum

(TF and QN of DRSE)

• It turns out this one doesn’t work• Signal and noise increases at once• Recall the situation with detuned RSE…

Summary• Ponderomotive amplifier based on optical lever

• Reduction of shot noise

• Strong against optical losses

• PA displacement noise is suppressed by spring

• Possible combinations: LIGO + MIT 1g IFO Virgo + LKB micro-mirror GEO + membrane TAMA + NAO 20mg IFO… etc.

End

Transfer function of signal/noise