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Towards dual recycling with the aid of time and frequency domain simulations
M. Malec for the GEO 600 team
Max-Planck-Institut für Gravitationsphysik
Albert-Einstein-Institut
AbstractDual Recycling has become a great challenge in terms of commissioning of GEO600. To achieve this, we need:
Frequency domain simulations (Finesse): Transfer functions or error signals within a huge parameterspace Equilibrium state of the detector
Time domain simulations (End to End Model): Interaction of optical, mechanical and electronical components of the experiment. Dynamic behaviour of the detector
Length control systemof GEO600
Errorpoint of the PRC feedback loop of dual recycled GEO600 for different tunings of the Michelson interferometer and two states of the SRC1. The plan is first to catch and lock the mirrors of the largely detuned detector and then continuously to tune the detector down to ~ 100 Hz.
1Hartmut Grote. Making it Work: Second Generation Interferometry in GEO600! PhD thesis, Max Planck Institute for Gravitational Physics, June 2003
Simplified dual recycling lock control scheme of GEO600. The modecleaners, partly actuators for the frequency feedback, are omitted for clarity.
Locking sequence:
1. light frequency (power recycling cavity
(PRC))
2. differential Michelson armlength (MID)
3. signal recycling cavity (SRC)
Institut für Atom- und Molekülphysik
Finesse is an interferometer simulation program that builds a set of linear equations representing an optical setup and solves them in the frequency domain, i.e. the system is always assumed to be in an equilibrium state. It can be used to calculate for example a transfer function from a mirror motion to the in-phase demodulated signal of a photodetctor at the interferometer output.1For further information please view http://www.rzg.mpg.de/~adf/.
Frequency domain simulations with Finesse
Transfer of the Schnupp sidebands to the photodiode for the MSR feedback in case of a tuned GEO600 detector.
Plans... ...with Finesse:Investigate the errorsignals with a different transmittivity of MSR of 5% (instead of 1%):
PRC control signal dependent on MSR position and Michelson differential tuning.
technical feasibility of moving from a largely detuned to tuned state: How closely can MSR be moved to the tuned case
position? gain and demodulation phase changes of SRC and MID Can there be any signal extracted from the detector for
an automatic gain control for the relevant control signals?
...with E2E
Implementation of SRC feedback. Tests and improvements of largely detuned dual recycling lock
acquisition with higher order modes. Seismic excitation of the mirror motion instead of discrete frequencies. Tests and improvements of the process of switching from detuned to
tuned dual recycling. Tests of dual recycling in case of MSR transmittivity of 5%.
Zerocrossings of the SRC errorpoint depending on the Schnupp modulation frequency.
Time domain simulations with End to End Model
The End to End Model (E2E) is a simulation program (developed by LIGO), that is able to describe a complete interferometer taking into account its optical, mechanical and electronical features1. 1For further information please view http://www.ligo.caltech.edu/~e2e/.
E2E calculates the output of subsystems in the time domain and was used to simulate the dynamic behaviour of a simplified GEO600 model.
Contact: [email protected]
Measurement with the power recycled GEO600 detector and the according E2E simulation. Only the PRC is locked.
A schematic overview of the simulated GEO600 experiment.
power recycling feedback on
Michelson differential feedback on
E2E simulation example of a PRC and Michelson lock acquisition.
SR tuning = 30 Deg.
ESD
IM
The 'real' triple pendulum suspension of the end mirrors MCe and MCn.
The virtual GEO600 setup created with the graphical user interface of E2E named ALFI.
SR tuning = 0 Deg.
MI errorpoint
PR refl. Power
BS power
PR refl. power
MID errorpoint
PR refl. power
Cavity power
MCn motion
Time [s]
Time [s]
PR refl. power
Cavity power
MCn motion
MCe motion
MPR motion
IM
IM
ESD
ESD
Mfn
MFe
MCn
MCeMPR BS
EOM3
EOM5Nd:YAG
MPR tuning [Deg.]MPR tuning [Deg.]
MI
tuni
ng [
Deg
.]
MID errorpoint slope SRC errorpoint slope PRC errorpoint slope
MSR tuning [kHz]
MSR tuning [kHz]
MID demodulation phase SRC demodulation phase
MSR tuning [kHz]
Dem
odul
atio
n ph
ase
[Deg
.]G
ain
[a.u
.]
Changes of the errorpoint slope and the demodulation phase of the feedback loops for MID, SRC and PRC moving the MSR position along the green line of the figure at lower left.
