Optical tables are a type of platform used by optical engineers and manufacturers to stabilize and support items during the process of testing, manufacturing, or repairing the optical elements that make up lasers, microscopes, and other optical devices. Designed to be extremely stiff and rigid, the use of an optical table is intended to minimize the effect of natural vibrations on the alignment of items/elements being examined or created.
During optical testing, even the slightest movement caused by floor vibrations can cause items to shift. Even the slightest nano millimeter of deviation from the intended placement of an item can render an experiment unusable.
As such, the use of an optical table (or suitable replacement) is standard in optics testing labs, manufacturing facilities, and repair centers.
Overview of Optical Tables
Optical tables are designed to hold optical components in perfect alignment, down to fractional measurements of mere nanometers. On regular and even anti-vibration tables, an individual walking by, a cart being rolled through a hallway, or the slightest flex of the table when you put a heavy object on top could destroy the experiment or force an engineer to begin again entirely.
When working on such a microscopic scale, the smallest and most seemingly insignificant vibrations can be like earthquakes, which is why optical tables were created.
Optical tables are extraordinarily rigid and unyielding, preventing any movement even as loads change or vibrations occur in the surrounding area. To ensure that any item placed on an optical table is perfectly balanced for optimal viewing and security during use, optical tables are carefully designed to be as perfectly flat as possible, completely level to prevent tipping or tilting in any direction, and equipped with mounts for optimal surface area to prevent rocking.
Some optical tables are designed with threaded attachment holes or magnets, used to secure mounts to the tabletop before being calibrated to the precise placement required for the experiment. To increase rigidity, optical tables are not made from the typical plastic, resin, or wood, but instead are made from thick sheets of carbon, steel, or aluminum.
Supporting the thick, rectangular metal tabletop are four legs, each reinforced with pneumatic vibration dampeners to accommodate virtually imperceptible changes in floor level.
Purpose of an Optical Table
Optical table design is highly purposeful, created to possess both static and dynamic rigidity and isolate/respond to vibrations. Typical workstations and lab tables may possess some of these qualities, but can’t provide the same unyielding stability as an optical table.
The purpose of an optical table is to create a stable surface on which to perform experiments, examine components, and create optical tools and equipment.
Here are the three key qualities that make this possible:
Dynamic rigidity resists external, typically vertical, vibrations like those that occur in the floor as a result of running heavy machinery or personnel walking around a facility. Dynamic rigidity helps to keep vibrations occurring below the table from affecting the surface by dampening vibrations and responding to changes in height or positioning. (See description of pneumatic isolators below.)
Static rigidity resists and dampens vibrations created by loads placed on the optical tabletop or created during an experiment. Static rigidity enables a tabletop to hold a steady, precisely calibrated alignment without disturbance. Static rigidity is a quality closely associated with high-frequency resonance.
Vibration Dampening & Isolation
Vibration dampening refers to the decrease in vibration frequency as it travels up through the floor, into the leg, and to the top of the table. Dampening features of optical tables gradually reduce vibrations to prevent them from disrupting positioning, a quality that is accomplished by adding pneumatic isolators to the legs of a table, which respond to varying vibration frequencies to provide real-time stabilization.
At first glance, an optical table may appear as nothing more than a chunky, sturdily built table or workstation thanks to its compact and unassuming design, but delving a bit deeper into the composition of these important tools, you’ll find a carefully refined and highly purposeful set of components.
Several types and variations of optical tables exist, but all can generally be broken down into three essential components: Top plate, body, and legs.
Typically made from aluminum or stainless steel, the top plate of an optical table must be extremely rigid and durable to accommodate frequent work and provide a solid, non-flexible work area that won’t warp or flex with changing loads. The top plate may be quite large – sometimes up to three meters – or smaller depending on the needs of a facility, but should always be made from a stiff, high-frequency resonance metal for optimal dampening.
In some high-heat applications, optical tables are outfitted with special thermal-treated plates to prevent heat-induced bending.
Most top plates are designed with a grid of threaded holes spaced evenly apart to accommodate various devices and platforms. Typically spaced between ½ an inch to an inch apart, and are outfitted to accommodate standard ¼ inch mounting screws.
Mounting holes do not run through the top plate and instead are sealed at the bottom to prevent components or small pieces from falling through. Optical tables not outfitted with threaded holes are typically magnetic clamp compatible for an alternative method of securing components.
The body of an optical table is the platform on which the top plate rests, and makes up the bulk of the table’s weight and function. Typically between 7 and 12 inches thick, the body is intended to provide additional support to the already rigid top plate to hold heavy objects and to reduce horizontal vibrations – like vibration created by machinery on top of the table.
Most optical table bodies are comprised of a combination of steel and additional dampening materials, providing extreme strength with superior vibration absorption.
The inner steel structure of the body typically resembles a honey-comb, designed to provide structural support without becoming unmovably heavy. Polymer foams, rubber, and other dampening materials are placed within the honeycomb structure, which helps to dampen outside vibrations and vibrations created by the experiment itself.
In some optical tables, the body may be outfitted with additional active dampening systems, which can detect a change in vibration frequency and respond accordingly.
The legs of an optical table are the final barrier to disruptive vertical vibrations, like those created by personnel walking around or adjacent running machinery. Small vibrations in the floor create vertical vibrations, which in turn change the height of the floor.
While these changes might be imperceptible to the human eye, the delicate experiments performed by optical engineers and researchers could easily be disrupted or destroyed by even the most minor movement.
To absorb vertical vibrations and keep the body/top plate of the table at a consistent, fully level height, optical table legs should be equipped with pneumatic isolators. Legs outfitted with pneumatic isolators contain two air chambers sealed by rubber diaphragms.
The chambers are connected by a small hole, which allows for the transfer of air. Rather than transferring perceptible vibrations upwards and to the body of the table, pneumatic isolator legs pass air from one chamber to the other, raising and lowering the table to keep the surface level.
Applications of Optical Tables
Optical tables are most commonly used for delicate processes like making prototype devices, examining small components, or performing technical and easily disruptable experiments. Designed to accommodate a variety of components that can be securely mounted to the tabletop, optical tables can be found in a wide range of facilities including laser laboratories, experimental and educational facilities, manufacturing plants, etc.