1. Thermal Compensation of the Radius of Curvature of GEO600 Mirrors
LIGO-G Z
Thermal Compensation of the Radius of Curvature of GEO600 Mirrors
H. Lück, S. Hild, S. Goßler and the GEO 600 team
Albert-Einstein-Institut für Gravitationsphysik
Institut für Atom- und Molekülphysik
Introduction
Optical Layout of GEO600
10W 1W
300W at
Beam Splitter 2W
98.65%
Laser
ROC = 687 m
Michelson Interferometer
Mode Cleaners
ROC = 666m
Power Recycling ~ mismatch in the Radius of Curvature (ROC) of the far mirrors  poor 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.
Compensation Concept
30W
71W
66W
60W
51W
74W
Dark Fringe vs. Heater Power
666 m
687 m
Intracavity vs. Dark Fringe Power
Far East Mirror & Heater
PRCImpedance matched
PRC Undercoupled
PRC Overcoupled
PRC reflected Power
Michelson Error Point