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Optical Tables, Introduction
Demands on the precision and resolutions
of metrologi cal equipment and
techniques have become more stringent
in pace with technological advances.
Metrological set ups and systems have
thus become more sensitive to external
influences, such as temperature variations
and vibrations.
Thermal effects may usually be minimized
by thermo stat ting, use of
temperature-compensated hardware and
supporting structures, shortening the
duration of mea sure ment, and other
relatively straightforward means. Special
equipment is available for minimizing
effects due to vibrations, but the full
benefits provided by such equipment will
be obtained only if all of the following
requirements are met:
••
All components of metrological setups or
systems must be sufficiently rigidly aligned
with respect to one another. This
requirement may be met by mounting all
such components on a single, extremely
stiff, base. Optical Table Tops are used for
this purpose.•
••
The entire complex, consisting of the experimental
setup itself plus its supporting
base, must be mounted on vibrationisolators.
Special supports equipped with
various types of vibration-isolation systems
are used for this purpose.
Compliance (mm/N)
Frequency (Hz)
Optical Table Tops
Optical Table Tops must be designed to
provide high structural stiffness if
relative motions of components mounted
on them due to external vibrations are to
be minimized. In addition, any vibrations
reaching Table Tops, in spite of the
vibration-isolation systems incorpo rated
into their supports, must be rapidly
damped out; i.e., Optical Table Tops must
have highly effective internal damping
mechanisms.
Optical Table Tops may thus be classified
in terms of their structural rigidities and
their internal damping cha rac teristics.
Their structural rigidities should be
assessed in terms of both their static
stiffness and their dynamic rigidities, i.e.,
their resistance to deformations due to
dynamic applied loads.
••
Their static stiffnesses are equivalent to
their Young‘s moduli, and are thus the
ratio of their bending deflec•tions to the
magnitudes of the temporally constant
(static), concentrated, applied loads
causing these deflections.•
••
Their dynamic rigidities, on the other
hand, express their Young‘s moduli as
functions of the frequencies of temporally
varying, i.e., dynamic, applied loads, such
as vibrations, inducing bending deflections
of their structures.•
The frequency responses of Table Tops
may be graphi cally represented in the
form of so-called „compliance“ curves,
defined as the reciprocals of their
dynamic rigi di ties, versus the frequencies
of periodically varying applied loads,
covering the full ranges of frequencies
likely to be of interest.
An analysis of the compliance curves of
Optical Table Tops indicates that they
may be roughly regarded as ideal rigid
bodies up to frequencies of about 80 Hz.
At higher frequencies, however, Optical
Table Tops exhibit resonances, evident by
occurrence of peaks in their compliance
curves. Compliance curves are a useful
aid in assessing the dynamic rigidities of
Optical Table Tops at various excitation
frequencies. They may also be used to
compare the frequency responses of
unloaded Table Tops of equal weight and
equal dimensions.
Since the amplitudes of vibrational
resonances of rec tang ular Table Tops are
greatest at their corners, corner-compliance
curves, or plots of their compliances
at their corners versus the frequencies of
dynamic applied loads, represent
quantitative indicators of table-top
per formance. The widths of resonance
peaks occurring in their corner-compliance
curves are indicative of the
effec tiveness of their internal damping
mechanisms.
In concluding our brief discussion of
these topics, we should emphasize that
the factors mentioned above refer to the
performance of unloaded Table Tops, i.e.,
to Table Tops with no components
mounted on them. These factors alone
are thus inadequate to fully describe
their performance under conditions of
actual use. Since the static loads, and
probably the dynamic loads as well,
exerted on Optical Table Tops by
experimen tal setups will vary from case
to case, purely qualitative design factors,
particularly specifications relating to
their honeycomb core mass density,
should also be taken into account in
selecting Optical Table Tops. The
material(s) used in fabricating their
honeycomb cores, core thickness, plus
specifications relating to their top and
bottom plates and their sidewalls,
constitute further major selection
criteria. Any design features or mechanisms
that have been incorporated in order
to improve their internal damping
characteristics should also be taken into
account.
Details of the special design features of
LINOS Photonics Optical Table Tops are
covered in the subsection entitled
„Design Features“.
Compliance curve for a typical Optical Table Top
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