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Dual Recycling in GEO 600. H. Grote, A. Freise, M. Malec for the GEO600 team Institut für Atom- und Molekülphysik University of Hannover Max-Planck-Institut für Gravitationsphysik 9. July 2003. Dual Recycling Concept. - PowerPoint PPT Presentation
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Dual Recycling in GEO 600
H. Grote, A. Freise, M. Malec for the GEO600 team
Institut für Atom- und MolekülphysikUniversity of Hannover
Max-Planck-Institut für Gravitationsphysik
9. July 2003
9. July 2003 Hartmut Grote
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
9. July 2003 Hartmut Grote
Adjustable Sensitivity
Frequency [Hz]
Str
ain
sens
itivi
ty [
1/sq
rt(H
z)]
Therm. noise
TMSR = 0,1%
TMSR = 1%
TMSR = 5%
9. July 2003 Hartmut Grote
Dual Recycling Configuration
PR cavity control (25kHz)
Michelson control (300Hz)
SR cavity control (400/40 Hz)
9. July 2003 Hartmut Grote
PR Error Signal
PR Tuning [Degree]
Mic
hels
on T
unin
g [D
egre
e]
9. July 2003 Hartmut Grote
Problem: Lock Acquisition
PR has to be locked first, but state space is limited
Lock Michelson in largely detuned SR state (larger state space)
MI optical gain depends on SR tuning
SR tuning [Degree]
Opt
ical
gai
n [A
rb.]
Michelson error signal
Signal Recycling error signal
9. July 2003 Hartmut Grote
SR Error Signal
Small capture range (0.5nm)
SR error signal is sensitive to various parameters
SR demodulation phase
Laser frequency with respect to PR cavity
Alignment
Michelson deviation from dark fringe
9. July 2003 Hartmut Grote
Michelson Deviation
MSR offset from operating point [nm]
SR
err
or s
igna
l [A
rb.]
0 nm
+1 nm
-1 nm
-2 nm
Michelsondeviationfrom dark fringe
9. July 2003 Hartmut Grote
Lock Acquisition
Dark fringe power
Intra cavity power
MI ESD feedback
MI slow feedback
SR error signal
SR feedback
MI error signal
9. July 2003 Hartmut Grote
Summary and Outlook
Established dual recycling lock at largely detuned operating point
Get more frequent acquisitions
Decrease pitch noise of pendulums
Normalize Michelson gain
“search“ for SR mirror by sweeping the operating point
Get stable DR locks including SR autoalignment
Tune signal recycling to nominal GW band in lock
9. July 2003 Hartmut Grote
9. July 2003 Hartmut Grote
Next Steps
PR + MI lockedPR + MI locked normalize MI gain to make system more robust during SR acquisitionnormalize MI gain to make system more robust during SR acquisition
simultanious ramping of SR modulation frequency and demodulationphase to search for SR fringe
simultanious ramping of SR modulation frequency and demodulationphase to search for SR fringe
Signal Recycling autoalignmentSignal Recycling autoalignment
Tuning down to GW band in lockTuning down to GW band in lock
9. July 2003 Hartmut Grote
MI error signal slope
Nominal operating points
Lock acquisition operating points
9. July 2003 Hartmut Grote
More experimental issues
SR error signal is sensitive to various parameters
SR demodulation phase
Laser frequency with respect to PR cavity
Alignment
Michelson deviation from dark fringe
9. July 2003 Hartmut Grote
9. July 2003 Hartmut Grote
Lock Acquisition
Dark fringe power
Intra cavity power
MI ESD feedback
MI slow feedback
SR error signal
SR feedback
MI error signal
9. July 2003 Hartmut Grote
9. July 2003 Hartmut Grote
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
9. July 2003 Hartmut Grote
Tuneable sensitivity
9. July 2003 Hartmut Grote
GEO Status July 2003
Michelson Interferometer
Laser
Mode Cleaners
2 W 1 W
~ 10 mW
300 W atBeam Splitter
MPR
final optics
test optics
MSR
9. July 2003 Hartmut Grote
Mode Healing
power recycling only:
Each recycling cavity minimises the loss due to mode mismatch of the respective other
with signal recycling:
9. July 2003 Hartmut Grote
Mode Healing
Mode healing
Mirror curvature compensation
MSR with T=1% yields almost perfectmode healing
9. July 2003 Hartmut Grote
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
9. July 2003 Hartmut Grote
SRC Error Signal
Example operatingpoint for 200 Hz detuning
9. July 2003 Hartmut Grote
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:
9. July 2003 Hartmut Grote
SRC Error Signal
Largely detuned operating point for lock acquisition
9. July 2003 Hartmut Grote
Detuned Dual Recycling
Zeit [s]
Michelson Ausgang
PR Resonator
Michelson Fehlersignal
ESD Feedback
IM Feedback
SR Fehlersignal
SR Feedback
9. July 2003 Hartmut Grote
Power Recycling
End mirrors with imperfectradius of curvature
beamsplitter: „tilt“motion
9. July 2003 Hartmut Grote
Power Recycling Signals