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Max-Planck-Institut für Gravitationsphysik Albert-Einstein- Institut Institut 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 Introductio n 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 71W 66W 60W 51W 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 m 687 m Optical Layout of GEO600 10W 1W 300W at Beam Splitter 2W 98.65% Laser ROC = 687 m Michelson Interferometer Mode Cleaners ROC = 666m Displacement [nm] 1.9 1.6 1.4 1.1 0.8 0.5 50. 3 0 Radius [cm] 9 4.5 0 -4.5 -9 0 5 10 z [cm] Temperature [°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
