Editing Optical table (section)

=== Materials and construction ===
Earlier optical table tops were sometimes made of a large slab of highly polished [[granite]] or [[diabase]].<ref name=Fisher>{{cite web |url=http://atap2.lbl.gov/LaserSafetyOfficersWorkshop/LSOW_PDF/5_1_Fisher.pdf |title=What you should know about optical tables |publisher=Newport |first=James |last=Fisher |page=2 |access-date=Oct 5, 2017}}</ref><ref name="Photonics.com">{{cite web |url=http://photonics.com/edu/Handbook.aspx?AID=25517 |title=Vibration Control |author=Newport Corporation |work=Photonics.com |access-date=Oct 18, 2012}}</ref> 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.<ref name=Fisher/><ref name="Photonics.com"/> 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]], [[aluminum]], or [[carbon fiber]], separated by a thick [[honeycomb structure|honeycomb]] 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 base]]s. Often, the table's legs are [[pneumatic]] vibration [[Damping ratio|damper]]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]]. One may also use a "[[flowbox]]", a device which produces a [[Laminar flow|laminar]] stream of air flowing downwards, kept at constant temperature by special [[air conditioning]].

The metal used to construct modern optical tables has a higher speed of sound than [[granite]] and therefore a higher frequency of the first [[eigenmode]]. Any vibration produced on the table below{{Dubious| reason=impulse response and harmonics|date=July 2014}} 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]]. [[viscosity|Viscous]] fluids are used in between the stiff materials, to aid in damping.