Dual Recycling for GEO 600

Andreas Freise, Hartmut Grote

Institut für Atom- und MolekülphysikUniversität Hannover

Max-Planck-Institut für Gravitationsphysik

27. March 2003

27. March 2003 Andreas Freise

Dual Recycling Concept

two recycling cavities enhance independently the carrier light and the signal sidebands

shot noise limited sensitivity is improved (typically by a factor of 102 to 103)

MPR

MSR

27. March 2003 Andreas Freise

Tuneable sensitivity

27. March 2003 Andreas Freise

GEO Status March 2003

Michelson Interferometer

Laser

Mode Cleaners

2 W 1 W

~ 10 mW

300 W atBeam Splitter

MPR

final optics

test optics

MSR

27. March 2003 Andreas Freise

Laser

Mode CleanersCommon arm length:(laser frequency stabilsation)

Pound-Drever-Hall

Dual Recycling Control

14.9 MHz

9 MHz

Differential arm length:(gravitational wave signal)

heterodyne detection Schnupp modulation

Signal-Recycling control: a separate modulation frequency reflected beam from AR coating

to laser frequency 37.2 MHz

27. March 2003 Andreas Freise

Power Recycling

End mirrors with imperfectradius of curvature

beamsplitter: „tilt“motion

27. March 2003 Andreas Freise

Power Recycling Signals

27. March 2003 Andreas Freise

From Power- to Dual Recycling

MPR

MSR

MI

Optical signals change because control sidebands and higher order TEM modes experience a coupled, 4-mirror cavity.

MI arm length difference: 10 cm cavity length difference: 9 cm

Transfer function for control sidebands must be maximised for various possible configurations:

27. March 2003 Andreas Freise

Mode Healing

power recycling only:

Each recycling cavity minimises the loss due to mode mismatch of the respective other

with signal recycling:

27. March 2003 Andreas Freise

Mode Healing

Mode healing

Mirror curvature compensation

MSR with T=1% yields almost perfectmode healing

27. March 2003 Andreas Freise

Control Sidebands (SR)

Resonance condition in the detuned, coupled, 4-mirror cavity:

fSR= 72 ·FSRSRC 9MHz

Detuning the modulation frequency and/orthe demodulation phase changes the SR operating point

27. March 2003 Andreas Freise

SRC Error Signal

Example operatingpoint for 200 Hz detuning

27. March 2003 Andreas Freise

SRC Error Signal

Largely detuned operating point for lock acquisition

27. March 2003 Andreas Freise

MI Error Signal Normalisation

Nominal operating points

Lock acquisition operating points

27. March 2003 Andreas Freise

Lock Acquisition

Dark fringe power

Intra cavity power

MI fast feedback

MI slow feedback

SR error point

SR feedback

MI error point

27. March 2003 Andreas Freise

Next Steps

PR + MI lockedPR + MI locked ramp MI gain to make system more robustramp MI gain to make system more robust

simulatnious ramping of SR modulation frequency and demodulationphase to search for SR fringe

simulatnious ramping of SR modulation frequency and demodulationphase to search for SR fringe

computer controlled lock acquisition of the autoalignment systemscomputer controlled lock acquisition of the autoalignment systems

27. March 2003 Andreas Freise