Dual Recycling for GEO 600 Andreas Freise, Hartmut Grote Institut für Atom- und Molekülphysik...
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Transcript of Dual Recycling for GEO 600 Andreas Freise, Hartmut Grote Institut für Atom- und Molekülphysik...
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