Test mass dynamics with optical springs proposed experiments at Gingin Chunnong Zhao (University of Western Australia) Thanks to ACIGA members Stefan Danilishin and Farid Khalili (Moscow State University) Yanbei Chen (Caltech) 1 GWADW2010, May 19, 2010

2 Contents: Gingin high optical power research facility 3-mode optomechanical transducer Test mass dynamics with double optical springs (negative optical inertia) Summary

GWADW2010, May 19, Gingin high optical power test facility High optical power is necessary for improving advanced detector sensitivity, but it also introduces thermal lensing and various instabilities.

GWADW2010, May 19, Gingin high optical power test facility On this facility, we have demonstrated: Thermal lesing and thermal compensation In-situ real time thermal lensing monitoring using Hartmann sensor 3-mode opto-acoustic interactions Cavity locking using ultra-low frequency vibration isolators Current main focus: parametric instability and its control

GWADW2010, May 19, Future 80m interferometer M1 M2 M3 To Detector Bench South Fabry-Perot Cavity East Fabry-Perot Cavity Mode Cleaner Nd:YAG laser = 1064nm East-end Station South-end Station N N Signal Recycling Mirror Beam Splitter Power Recycling Cavity

GWADW2010, May 19, Currently, 2 independent 80m cavities South arm: Sapphire test masses with LIGO SOS suspension Finesse, ~1300, 10 W laser Tested thermal lensing and thermal compensation; Observed 3-mode opto-acoustic interactions; Study 3-mode optomechanical transducer. East arm: Fused silica test masses with UWA isolators and suspensions Nominal cavity finesse, W laser to be installed in August Main goals are test the parametric instability and its control.

GWADW2010, May 19, mode optomechanical transducer Test mass internal mode  m Cavity Fundamental mode (TEM 00, frequency  o ) Input light frequency  o Scattering into TEM mn, frequency  1 frequency matching and spatial overlap of acoustic and optical modes

GWADW2010, May 19, FSR   TEM 3-mode optomechanical transducer 00  0 +  m  TEM

GWADW2010, May 19, CO 2 laser thermal tuning the radius of curvature Sapphire test mass Hartmann sensor He-Ne laser CO 2 laser Probe beam (800nm) Vacuum tank Vacuum pipe Nd:YAG laser

GWADW2010, May 19, CCD Laser ITM CP ETM Spectrum Analyzer y x QPD Fundamental mode High order mode 3-mode optomechanical transducer CO 2 Laser

GWADW2010, May 19, Test mass thermal noise at ~181.6 kHz 3-mode optomechanical transducer

GWADW2010, May 19, mode optomechanical transducer potential to observe the quantum radiation pressure noise Laser 1mm x 1mm x 50nm The vibration of silicon nitride membrane excites high transverse optical mode QPD Finesse=10,000 Meff=40 ng, T=4 k,  m=2  *200 kHz Qm=10 6 Circulating power= 0.5W Radiation pressure noise ~ thermal mechanical resonance

GWADW2010, May 19, Test mass dynamics with optical springs Motivation: The SQL in terms of GW strain sensitivity: A system with larger mechanical susceptibility (  /m) has smaller SQL than the free mass SQL Y. Chen, et al, LIGO-T v1

GWADW2010, May 19, Test mass dynamics with optical springs Considering the test mass dynamics with double optical springs (DOS) F is the force applied on the test mass, x is the displacement,, Here, s=-i  ;

GWADW2010, May 19, Test mass dynamics with optical springs PM: power recycling mirror; PBS: polarization beam splitter; BS: beam splitter; PD: photodetector; ITM: input test mass; ETM: end test mass. Driving force This is achievable at Gingin with a 3-mirror cavity: The same configuration can also be used to demonstrate the local readout (optical bar)

GWADW2010, May 19, Test mass, m=0.8 kg, cavity length L=80m, cavity circulating power: I 1 = 3kW, I 2 =10kW, Cavity detuning:  1 /2  =200 Hz  2 /2  =-500 Hz Cavity linewidth:  1 /2  =36 Hz;  2 /2  =400 Hz; Test mass dynamics with optical springs Free mass With DOS

GWADW2010, May 19, Summary Gingin high optical power research facility consists: High power lasers Advanced vibration isolators and test mass suspension High finesse cavities In addition to the parametric instability research, we propose to study: High sensitivity optomechanical transducer (potential for detecting the quantum radiation pressure noise) Optical negative inertia Local readout (optical bar)