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An optical table is a
vibration control In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures. All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybri ...
platform that is used to support systems used for
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
- and
optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...
-related experiments in
science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...
,
engineering Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...
and
manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary sector of the economy. The term may refer ...
. The surfaces of these tables are designed to be very rigid with minimum deflection so that the alignment of optical elements remains stable over time. Many optical systems require that vibration of optical elements be kept small. As a result, optical tables are typically very heavy and incorporate vibration isolation and damping features in their structure. Many use pneumatic isolators that act as mechanical
low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filt ...
s, reducing the ability of vibrations in the floor to cause vibrations in the tabletop. Optical tables that use pneumatic isolators are sometimes called air tables. The surface of an optical table is typically
stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...
with a rectangular grid of tapped holes in either metric or imperial units: * metric: M6 on a 25 mm grid * imperial: ¼"-20 UNC on a 1" (25.4 mm) grid Optical breadboards, benches, and rails are simpler structures that perform a similar function to optical tables. These are used in teaching and in
research and development Research and development (R&D or R+D), known in some countries as OKB, experiment and design, is the set of innovative activities undertaken by corporations or governments in developing new services or products. R&D constitutes the first stage ...
, and are also sometimes used to support permanently aligned optical systems in finished devices such as lasers.


Explanation

In optical systems, especially those involving
interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...
, the alignment of each component must be extremely accurate—precise down to a fraction of a
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
—usually a few hundred
nanometer 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling Despite the va ...
s. Even small vibrations or strain in the table on which the elements are set up might lead to complete failure of an experiment. Hence, one requires an extremely rigid table which neither moves nor flexes, even under changing loads or vibrations. The surface of the table must also be quite flat, to allow precision optical mounts to make good contact with the table without rocking and facilitate easy assembly of the optical system.


Materials and construction

Earlier optical table tops were sometimes made of a large slab of highly polished
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
or
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-gra ...
. These materials are very dense and stiff, which inhibits flexing and motion of the surface, improving the stability of the optical system. The surfaces can be ground extremely flat, which is beneficial for alignment of optical systems. Such tables were very heavy and expensive, however, and did not do a good job of damping vibrations. Mounting components to a granite surface is also difficult. Granite and diabase are still used for smaller precision-flat surfaces, but optical tables made from these materials are not commonly available today. Modern optical tables are typically made of top and bottom sheets of
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
,
aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
, or
carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers ( Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon comp ...
, separated by a thick
honeycomb A honeycomb is a mass of Triangular prismatic honeycomb#Hexagonal prismatic honeycomb, hexagonal prismatic cells built from beeswax by honey bees in their beehive, nests to contain their brood (eggs, larvae, and pupae) and stores of honey and pol ...
lattice structure. The surface usually has a grid of threaded holes which allow the components to be bolted down to fit the optical system layout. Components may also be held to the steel surface by magnetic bases. Often, the table's legs are
pneumatic Pneumatics (from Greek 'wind, breath') is the use of gas or pressurized air in mechanical systems. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A centrally located a ...
vibration
damper A damper is a device that deadens, restrains, or depresses. It may refer to: Music * Damper pedal, a device that mutes musical tones, particularly in stringed instruments * A mute for various brass instruments Structure * Damper (flow), a mech ...
s. For even more accurate setups, one also prevents air movements and temperature gradients by enclosing the surface in a box of transparent plastic such as
Plexiglas Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bra ...
. One may also use a " flowbox", a device which produces a laminar stream of air flowing downwards, kept at constant temperature by special
air conditioning Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...
. The metal used to construct modern optical tables has a higher speed of sound than
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
and therefore a higher frequency of the first
eigenmode The mode of electromagnetic systems describes the field pattern of the propagating waves. Some of the classifications of electromagnetic modes include; * Modes in waveguides and transmission lines. These modes are analogous to the normal modes of ...
. Any vibration produced on the table below this frequency does not produce a resonant response, making the setup less sensitive to vibrations from motorized optics, cooling water pumps, etc. Vibration damping may be added to tables during their construction. As with granite's composite structure, the combination of several stiff materials with different speeds of sound produces a table for which a wide range of vibrations are
critically damped In physical systems, damping is the loss of energy of an oscillating system by dissipation. Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. Examples of damping include ...
.
Viscous Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for example, syrup h ...
fluids are used in between the stiff materials, to aid in damping.


Breadboards

An alternative to an optical table is an optical breadboard. Some optical systems use breadboards made of solid aluminum for later integration with a larger system with some form of vibration control. Most optical breadboards are constructed from steel, aluminum, or carbon fiber sheets with honeycomb structure and can be placed on an ordinary table or workbench. Breadboards are not as good as optical tables, but weigh less and are adequate for smaller optical systems that do not require extremely high levels of mechanical stability. The low weight enables one to support these tables on soft air springs which reduce vibrations coming from the floor, although this increases vibrations due to acoustic noise. The honeycomb structure reduces bending due to the breadboard's own weight, so it can be tilted and forces applied via the soft spring supports accelerate the table as a whole without misalignment. Breadboards can therefore be used in mobile applications, such as on airplanes. Also, one can bolt a breadboard onto an optical table, build up a module of the experiment on it, and then transfer the module as a whole onto another table without the need to realign the components on the breadboard. Similarly, custom-built optical devices are assembled and aligned on breadboards, which are then enclosed in a case and shipped to the customer.


Rails and benches

An optical bench or optical rail is a simpler piece of hardware that provides a linear (or sometimes curved) track along which to mount optical elements. They are often used for simple experiments, especially for classroom demonstrations. Such rails are typically made of steel and designed to be very stiff, with features that allow holders for optical components to be bolted down and easily shifted along the length of the rail. Rails are common in laser assemblies where the beam path travels on a single axis. A more sophisticated example is the
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...
ceramic toroidal optical bench in the Gaia spacecraft (illustrated), which supports several optical instruments.


See also

* Optical cage system


References


External links


Optical table simulator

Fundamentals of Vibration Isolation for Optical Tables
{{DEFAULTSORT:Optical Table Laboratory equipment Tables (furniture) Table, optical