Low frequency - high sensitivity horizontal monolithic Folded-Pendulum as sensor in the automatic control of ground-based and space telescopes

We describe a new mechanical implementation of a monolithic folded pendulum based inertial sensor, configurable as seismometer and as accelerometer. The sensor is a compact, light, fully scalable, tunable in frequency (< 100mHz), with large measurement band (10(-6) Hz divided by 10Hz) and high quality factor (Q > 1500 in air) instrument, with immunity to environmental noises guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical one (10(-12)m/root Hz) in the band (0.1 divided by 10Hz). Although its natural application is in the fields of earthquake engineering and geophysics, its performances make it suitable also for applications as sensor in the control of inertial platforms for interferometric detectors of gravitational waves, where a residual horizontal motion better than 10(-15)m/root Hz in the band 0.01 divided by 100Hz is a requirement, and in the control of the mechanical support systems of ground-based or space telescopes.