Summer 1998: Progress Report
The experiments on dual recycling at the Garching prototype worked very well. The dual recycling lock was extremely stable. The trickiest part of the experiment was manual alignment of signal recycling even when aided by auto-alignment. The signal enhancement was improved by optimising the demodulation phases and the modulation frequency. The signal recycling led to a significantly larger contrast of the interferometer. The agreement between our model and the measured signal sizes and modulation frequency is good. These experiments show that dual recycling can be used to improve the performance of GEO 600.
Both tubes have been resuspended using stainless steel wires. The pressure in the eastern tube is already in a region that is low enough. At the ends of the tube it is in the mid 10-9 mbar region with a clear air signature.
The mode-cleaner vacuum system is ready for a bake-out (70 to 80 °C for four days).
No fairy tale: A mouse built a nest in the glass-fibre cable tray and the inmates munched through the whole bundle. We try to repair it by installing plugs at the free ends. (We are in search of a pest controller...)
The northern tube has been wrapped with rockwool. Even when wrapped possible leaks can be detected "easily" enough by means of a helium leak test.