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