Theory of Vibration Isolation Vibration isolation or elimination on an optical surface is a
two-part problem. As discussed previously, an optical tabletop is
designed to have zero or minimal response to a deflective force or
vibration. This in itself is not sufficient to ensure a vibration-free
working surface. The rigid tabletop may still vibrate without deforming
(i.e., vibrations of the table on the mounting system). These
vibrations are constrained translations and/or rotations of the optical
Typically, the entire table system is subjected continually to
vibrational impulses from the laboratory floor. These vibrations
may be caused by large machinery within the building or even by
wind or traffic-excited building resonances (swaying).


Vibrations of a floor in a building can be divided into two basic
components: vertical and horizontal. Typically, vertical components
range from 10 to 50 Hz, and horizontal components range
from 1 to 20 Hz. To prevent such vibrations from disturbing an
experiment, it is important to mount the table in such a way as to
isolate it vibrationally from the laboratory floor (i.e., mount the
table in such a way that its instantaneous position is independent
of the periodic motions of the laboratory floor). This type of isolation
is termed “seismic” mounting. When an object is truly seismically
mounted with respect to the floor, the motions of the object
and the floor are completely uncoupled and separate. The term
seismic is linked with the study of earthquakes, in which the magnitude
of an earthquake is estimated from the motion of the ground
with respect to a seismically mounted indicator.

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