The GEO 600 gravitational wave detector is currently under constructio
n in Germany. To ensure that the detector sensitivity is not limited b
y seismic noise above 50 Hz a significant degree of seismic isolation
has to be provided for each test mass. To achieve this level of isolat
ion each test mass, which will be made from fused silica (mass similar
to 14 kg), will be suspended as the final stage of a triple pendulum
from an isolation stack consisting of layers of stainless steel masses
and graphite loaded silicone rubber. Extending from the stack will be
three cantilever springs supporting an upper mass from which a double
pendulum stage will be suspended. This double pendulum will incorpora
te cantilever springs in the upper stage in order to enhance the verti
cal isolation, and will use fused silica fibers in the lower pendulum
stage in order to minimize thermal noise from the pendulum modes. The
expected performance from this arrangement of stacks, vertical spring
stages, and double pendulums should achieve our goals for seismic isol
ation. (C) 1998 American Institute of Physics.