What is an Optical Table?
Optical Table and Breadboard products are designed to provide a large, vibration isolated and damped work surface from which to conduct optical experiments. An optical table consists of two main items: support and an optical tabletop or breadboard. The support can be in the form of a frame with casters or as four individual cylindrical legs. The supports can be either elastomeric (rigid) with nominal vibration isolation or pneumatic, which provides the best isolation from floor vibrations. The tabletop has a matrix of 1/4-20 or M6 threaded holes on the surface and is constructed with a steel honeycomb structure to make it stiff, but with minimal mass. The vibration control provided by optical tables is frequently used in applications such as microscopy, metrology, optical fibre alignment, interferometry, or wherever optical experiments are done. Optical tables can be found in just about any laser lab but also support bio-medical, life sciences, astronomy, metrology, and semiconductor industries.
What Does an Optical Table Do?
An optical table is a vibration control platform that is used to support systems used for laser- and optics-related experiments, engineering and manufacturing. 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 is 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 filters, reducing the ability of vibrations in the floor to cause vibrations in the tabletop.
The surface of an optical table is typically stainless steel 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 and are also sometimes used to support permanently aligned optical systems in finished devices such as lasers.
What is an Optical Table Used For?
In optical systems, especially those involving interferometry, the alignment of each component must be extremely accurate—precise down to a fraction of a wavelength—usually a few hundred nanometers. Even small vibrations or strain in the table on which the elements are set up might lead to the 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.
How Does an Optical Table Work?
Broadband damping absorbs and dissipates vibration energies across a broad range of frequencies. It is widely used in anti-vibration tables to reduce the structural vibrations of the tabletop. Typically the broadband damping involves energy absorption materials such as foam, rubber or elastomers. It may also involve mass blocks/plates and rubbers installed along the side of the table to absorb a moderate amount of vibrations for a broad frequency range that covers the resonances of a standard size optical table. Broadband damping does not target any specific table resonance or any specific set of frequencies; instead, it absorbs and dissipates vibration energies uniformly across the frequency range. It is usually affordable and good for applications that do not require high damping performances.
Tuned Mass Damping (TMD)
A tuned mass damper is a device consisting of a mass, a spring, and a damper that is attached to a structure in order to reduce the dynamic response of the structure. It is tuned to a particular structural frequency so that when the table50100 resonance is excited, the damper will resonate out of phase with the structural motion of the structure. Vibration energy is then dissipated by the damper inertia force acting on the structure. TMD is the most effective method among all known passive damping methods, as it concentrates damping efforts where it's needed at the frequencies of dominant resonance modes. It is widely used in various industries for its efficiency and effectiveness of damping, such as the famous Grand Canyon Skywalk, Taipei 101 Building, and NASA's Ares I rocket. Different from broadband damping which absorbs a moderate amount of vibration energy equally over the broadband, TMD targets resonances and as a result is much more effective.