Design and Evaluation of A Simple Ultralow Vibration Vacuum Environment
John R. Lawall, Ernest G. Kessler
A vibration-isolated platform in a high-vacuum environment designed for prototyping optical interferometers is described. The system provides isolation from both seismic and acoustic disturbances with a residual acceleration of 2.9 x 10-6 m/s2 rms (root-mean-square) in the vertical direction and 6.3 x 10-6 m/s2 rms in the horizontal in the bandwidth from 5 to 400 Hz. The environmental decoupling provided by the spring suspension, air-spring table legs, and vacuum are evaluated sequentially to illustrate the effects of each. The vibration contributed by the turbomolecular pump is measured and shown to fall into a low-frequency zone from 26 to 76 Hz as well as peaks at the pump rotation frequency of 820 Hz and its harmonic at 1.64 KHz. The low-frequency noise arising from the pump is less than 2% of the total residual acceleration in the bandwidth from 0.25 to 400 Hz. The platform is used to construct a high-finesse open-cavity Fabry-Perot interferometer, using standard commercial mounts, with relative motion below 2 pm rms in a 3 kHz bandwidth. Of this motion, the contribution due to the pump at 820 Hz is only 0.3 pm. The acoustic decoupling provided by the vacuum environment allows experiments that are prohibitive at atmospheric pressure even in a tightly sealed enclosure.