Max-Planck-Institut für Gravitationsphysik
Albert-Einstein-InstitutInstitut für Atom- und Molekülphysik
Thermal Compensation of the Radius of Curvature of GEO600 Mirrors
H. Lück, S. Hild, S. Goßler, K. Kawabe and the GEO 600 team
Introduction Power Recycling ~2000 + mismatch in the Radius of Curvature (ROC) of
the far mirrors poor contrast @ beam splitter. Poor contrast degrades error signals and makes locking impossible. GEO600 far mirrors have a mismatch in ROC of about 3%. Thermal gradient created by a ring heater deforms the mirror and corrects
the ROC.
Far East Mirror & Heater
30W
71W66W
60W51W
74W
Dark Fringe vs. Heater Power
Compensation Concept
PRCImpedance matched
PRC Undercoupled
PRC Overcoupled
Michelson Error Point
PRC reflected Power
Michelson Error Point
PRC reflected Power
Intracavity vs. Dark Fringe Power
666 m687 m
Optical Layout of GEO600
10W 1W
300W atBeam Splitter
2W
98.65%
Laser
ROC = 687 m
Michelson InterferometerMode Cleaners
ROC = 666m
Displacement [nm]
1.9 1.6 1.4 1.1 0.8 0.550.3 0
Rad
ius
[cm
]
9
4.5
0
-4.5
-9
0 5 10
z [cm]
Tem
pera
ture
[°C
]
45
40
35
30
25
Analytical calculation of the temperature distribution in the mirror substrate
Results from Finite Element Analysis of the mirror expansion
Simulation Results
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