Advanced equipment and processes have made it possible to investigate phenomena with dimensions measured in nanometers. For example, phase-shifting optical interferometers can now measure surface roughness with a resolution of about 1 nm. In the semiconductor field, integrated circuits with submicron line widths are now being produced. Applications like these have created the demand for equally innovative vibration isolated support structures which provide the stability needed for such measurements and processes. Successfully meeting this level of stability requires careful attention to the problems of maintaining extremely precise relative alignment of the various elements of the system.
Vibration can be a limiting factor in the performance of a wide variety of research and production applications. Vibration is all around us, from HVAC environmental sources to road vibration and other unavoidable “background” vibrational noise – we live in a noisy, vibrating world! Consider the task of photographing a highly magnified image. The microscope and camera optics together determine where on the film plane each point of the object is imaged. During the exposure time, if every point of the optical system – illuminator, sample, microscope optics, camera optics and film plane – moves simultaneously with no relative motion, the image will be clear. On the other hand, if there is relative motion of the sample with respect to the objective lens, the image will be blurred. Further, if an experiment uses elements that mechanically move or vibrate, it’s important that these elements can be vibrationally isolated, as not to disturb other optical elements that are already aligned, in the same area. This issue is critical to the success or failure of delicate, vibrationally-sensitive optical experiments.
Since the sources of vibrational disturbances cannot completely be eliminated, the goal is to reduce relative motion between elements by connecting them with a structure that is as rigid as possible.
In a perfectly rigid body, theoretically, the distance between any two points remains constant in time. This means that the size and the shape of the body do not change while it is undergoing force inputs from vibrations, static forces or temperature changes. If all of the elements are mounted together to form an ideal rigid body, the individual elements will not move relative to one another and system performance will not be impaired.
Since it is impossible to create a perfectly rigid structure, an effective vibration isolation system must take into consideration these factors:
Dynamic Forces (Vibration)
Dynamic forces cause structural deformations that vary with the frequency of the driving force. Structural resonance can amplify the relative motion between optical components.
Static Forces
Static forces cause deformations that are constant in time. However, the addition or movement of equipment in the system will change the static forces and cause misalignment of system elements.
Temperature Effects
Non-uniform temperature changes usually cause a slow bending of the structure, with time constants of one hour or more. The key techniques for reducing thermal effects are:
Newport pioneered the invention of the honeycomb optical bench and continues to produce the finest vibration control systems available for nano-technology applications. Newport advanced isolation systems offer the best vibration filter systems available. Super rigid honeycomb structures further minimize relative platform motion due to dynamic, static and thermal forces. Unsurpassed attention to detail and quality places Newport optical benches in a class of their own.
Optical tables provide a rigid platform for high-precision optical experiments and systems. They are designed to eliminate errors caused by relative motion between optical components in the beam path. Rigidity is the primary consideration in optical table design. Table rigidity can be quantified in terms of static or dynamic rigidity.
Honeycomb is commonly used to produce very low weight, highly rigid structures. Reduced weight dramatically improves the dynamic rigidity of the structure by moving structural resonance modes to higher, less detrimental frequencies. The structural resonance modes are the frequencies at which the platform deflects, therefore causing relative motion across the optical mounting surface. For a given input vibration force, the deflection is reduced as the mode frequency increases. This is the primary reason why steel honeycomb has replaced granite in most high-end optical applications - since granite is relatively heavy, the resonance modes occur at lower frequencies and therefore produce higher amplitudes of surface deflection.
Trussed Core Design - Newport innovated the trussed core design to maximize the table's rigidity-to-weight ratio. The trussed core design uses an additional steel member to bridge across the center of the honeycomb cell. This extra mechanical component significantly stiffens the cell, with very little increase in weight. The truss improves both the static and dynamic rigidity and increases the structure's point load carrying ability. Many manufacturers use a traditional open cell construction, which is not as statically rigid, when compared to a Newport table.
Vertically Bonded Core - All Newport tables are vertically bonded along the height of the honeycomb core. Most other manufacturers forego this extra step because of added expense and time required to apply adhesive to each individual core member. However, vertical bonding is the most important step to maximize the table's rigidity-to-weight ratio. An additional benefit is the introduction of constrained layer damping effects into the core construction.
Triple Core Interface - The trussed core design enables a triple core interface at each honeycomb cell. Whereas open core designs only have two structural members at each interface, the Newport table has three. Since most manufacturers use 0.010 thick steel sheet, their core interface has a thickness of 0.020 inches. The Newport design offers a 50% increase in local rigidity by using a 0.030 inch support member. Additionally, the three sheets are fully bonded for the full table height producing greater stiffness and constrained layer damping.
Custom Cores - Newport offers the greatest experience and core selection available. Newport commonly builds trussed cores in several sizes, open aluminum cores for very lightweight structures and perforated cores for high vacuum or cleanroom applications. Other constructions include egg crate and tubular structure designs. This allows extending Newport's capabilities beyond optical tables to build honeycomb towers for drawing optical fibers, vertical systems for large laser beam lines, pedestal flooring systems for semiconductor manufacturing equipment and a large variety of instrument platforms, gantries and bridges.
Beam path stability is a primary requirement for many optical experiments and processes. Newport meets the challenges of leading edge nano-technology by offering the best surface flatness and thermal stability available in a honeycomb structure. Whereas other manufacturers seek to make tables more quickly, Newport takes the extra steps to focus on making the best.
Precision Bonding Platens - Metrology quality steel assembly platens are used to ensure the superior flatness of our optical tables. The platen supports the top surface of the table during the assembly and bonding process and imprints the top surface with the same flatness characteristics. Routinely verified with optical interferometers, these platens are the largest and flattest in the industry. These platens allow Newport to build the world's largest optical tables.
Gravity Pressure Bonding - Applying constant pressure across the optical table during the bonding process ensures that the top surface conforms to the platen flatness. Newport uses gravity pressure bonding to control the load across the table surfaces and to ensure process consistency from table to table. Other manufacturers use hydraulic presses to speed up the assembly process. However, the hydraulic pressure must be monitored for consistency and may apply uneven forces across the table top.
Low Thermal Stress Bonding - Slow curing of the table bonds at room temperature is critical both to maintain table flatness and ensure long term stability of the table structure. Fast curing adhesives heat the core and lock thermal stresses into the table. Some manufacturers apply heat to the table to improve their production cycle times. Temperature induces stress causing the table to bow when it is returned to room temperature. Temperature curing can also induce long term bowing, and in extreme cases delamination of the core, top or bottom surface. Newport's slow cure method takes longer but allows production of the flattest tables available. Newport also provides a lifetime guarantee against delamination with each table.
Super Invar and other Advanced Materials - Newport has more experience with advanced materials than anyone else in the optical table industry. Newport's long relationship with the Aerospace industry and advanced labs all over the world has given the Newport Vibration Control team unsurpassed materials capabilities. Newport is the premier supplier of Super Invar tables for the absolute leading edge of optical research. Super Invar exhibits almost no thermal expansion near room temperature. Newport also has extensive experience with very light, highly stable carbon structures. For the ultimate in flatness, Newport can also provide granite platforms, granite/-epoxy composites or granite/honeycomb composites.
Experimental or process disturbances caused by relative motion between optical components generally occur at the structural dominant bending or torsional modes. In addition to pushing these natural modes to higher, less detrimental frequencies, a major advantage of honeycomb over granite is the high level of damping present in the honeycomb structure. Damping attenuates the amplitude of the natural modes and reduces the relative motion across the table surface. In very precise applications such as optical interferometry, maximizing the table's damping properties is absolutely critical.
Three types of damping are used for optical tables: Narrow Band Tuned Damping, Broadband Tuned Damping and Constrained Layer Broadband Damping. Newport is the only company that offers all three forms of damping in a single optical table.
Narrow band tuned dampers can only be found in Newport RS Series tables. Newport carries in stock over 200 individual dampers plus damp modes from 20–480 Hz. A trained vibration engineer tests each table to determine the natural modes of the structure.
Narrow band vibration absorbers are then selected to eliminate these modes and installed in the highest amplitude position (usually the corners). Different grades are available to offer varying levels of damping. In applications where heavy payloads can significantly effect the structural modes of the table, Newport can simulate the load and optimize the tuned damping. When damping doubler systems, where two or more tables are rigidly connected, the tables are assembled and tuned as a monolithic structure.
Optical laboratories and high technology industries require high levels of product cleanliness.
| Feature | Benefit |
|---|---|
| Trussed core design | Better rigidity-to-weight ratio Better static rigidity Better dynamic rigidity Increased point load carrying ability |
| Vertically bonded core | Better rigidity-to-weight ratio Better static rigidity Better dynamic rigidity Increased point load carrying ability |
| Triple core interface | Better rigidity-to-weight ratio Better static rigidity Better dynamic rigidity Increased point load carrying ability |
| Low thermal stress bonding | Improves table flatness Eliminates long term table bowing Guarantees non-delamination |
| Narrow band tuned damping | Most effective method of eliminating specific vibration modes Much more effective than broadband at low resonance frequencies |
| Broadband damping | Reduces the amplitude of vibration modes across broader frequency ranges More effective than constrained layer over specific frequency bands |
| Damped top skin | Reduces ringing of work surface |
| Individually sealed holes | Prevents liquid spill from moving to other honeycomb cell locations or contaminating the table interior |
| Non-corrosive sealed holes | Prevents long-term table degradation from corrosive liquid spills |
Newport invented the Stabilizer™ isolator and introduced a new level of vibration isolation to the scientific industry. The Stabilizer™ features Newport's proprietary hybrid chamber and laminar flow damping system to provide isolation from even the lowest amplitude vibrations. When used with extremely rigid tuned damped tables, Newport optical bench systems offer unmatched performance. It is no wonder most leading edge researchers will only accept Newport in their laboratories.
Pneumatic isolators filter vibration before the mechanical noise can reach the optical bench work surface. Improved vibration isolation reduces errors caused by relative motion between optical components in the beam path. Pneumatic isolators combine with the optical table and payload to form a mass/spring/damper system. Pneumatic systems are used instead of mechanical springs since they offer self-leveling and minimize the effect of varying mass on isolation. The performance of the isolator is defined primarily by its natural frequency and damping characteristics:
Conventional isolators use a compliance chamber to act as an air spring and a damping chamber to increase system stability. The two chambers are connected through a thin tube or orifice.
Newport's proprietary Stabilizer™ design offers a unique and greatly improved approach to isolator design. The Stabilizer™ provides significantly more damping of the natural frequency amplitude due to the closer coupling of the piston and damping element. The result is improved isolation and better stability when compared to conventional isolators.
The natural frequency of a pneumatic isolator decreases as the compliance volume increases, thereby improving the isolation performance. The hybrid chamber design maximizes the compliance volume; Ultra-soft diaphragms reduce the stiffness limitation.
Pneumatic isolators commonly use valves to stabilize and relevel the optical table after disturbance. Three two-way valves are supplied with each Newport system to control the platform in three degrees of freedom (vertical, pitch and roll). The valve is mounted to the isolator and senses the floating platform height with a lever arm. As the table is disturbed the lever arm moves and actuates the leveling valve to add or exhaust air in the pneumatic isolators as required to maintain platform height. Air is only supplied when the system is releveling.
Newport manufacturers its own custom valve designed specifically to meet the needs of optical table users. Other manufacturers use less than optimal off-the-shelf valves and cannot offer high accuracy releveling. Only 3 leveling valves are required regardless of the number of isolators in the system.
The pneumatic isolator offers isolation in the vertical direction; horizontal isolation is achieved through a mechanical filter system. Many manufacturers use some form of a bearing surface to provide a pivot or rolling surface for vibration filtering. However these contacting systems always have mechanical defects and surface roughness between the bearing surfaces. The bearing surface introduces frictional noise and limits the isolation of very low level vibrations that commonly disturb high accuracy systems.
Trifilar Pendulum - Newport uses a frictionless trifilar pendulum system for horizontal vibration isolation. The natural mode of the pendulum is very low in frequency, typically 1 to 2 Hz depending on the length of the pendulum. Above the natural frequency the pendulum isolates vibration. Since the system operates by flexing, it offers no frictional resistance to motion and can isolate very low amplitude mechanical vibration.
Viscous Damping - The natural frequency of the pendulum is damped using low vapor pressure oil. This system offers a significant decrease in the amplitude of the natural mode without adding higher frequency frictional noise.
Newport has refined our laboratory grade pneumatic isolator for many years and offers a variety of features not found in imitative products.
| Feature | Benefit |
|---|---|
| Hybrid chamber design | Lowest natural frequency offers maximized isolation bandwidth Optimized damping capability Compact design is 30% smaller than conventional isolators Improved isolator responsiveness Improved high center of mass stability |
| Less amplification at resonance Improved setting time Very little effect on isolation bandwidth Adjustable damping for special applications |
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| Ultra-soft diaphragms | Improved low frequency isolation Improved isolation of low amplitude vibrations |
| High accuracy leveling valves | More accurate leveling of table Improved repositioning of table after disturbance Allows table-to-table beam pointing applications |
| Airflow control valves | Allows optimization of pneumatic control |
| EAR gain arm interface | Decouples sensor arm vibration from table Better leveling accuracy Does not degrade like foam pads |
| Trifilar pendulum horizontal isolation | Zero-friction design enables isolation to much lower vibration levels Improved re-positioning after table disturbances |
| Self centering | Ensures isolator alignment Eliminates horizontal shorting |
| Height adjustment | Adaptable to uneven floors Allows alignment of separate tables |
| Modular support bases | Allows system height to be field modified Allows field integration of tie-bar caster system |
| Free standing design | Better isolation performance Eliminates structural resonances found on tie-bar systems Adaptable to uneven floors |
Yes. Newport uses a trussed core design that, although lighter than competitive cores, actually exhibits better static rigidity. The higher rigidity is due to the vertical bonding provided at the triple core interface. Other manufacturers forego the production expense of bonding along the height of their core resulting in a core that is both heavier and less rigid. The lighter Newport trussed core is also dynamically superior due to the higher stiffness-to-weight ratio.
Narrow band tuned damping techniques are far more effective than broadband dampers. Narrow band dampers selectively eliminate the vibration mode. Different dampers can be used for different modes and are effective for damping mode harmonics. Narrow band dampers are individually chosen for the table geometry and are not affected by table loads up to 25% of the table mass. Tables with heavier loads can be custom tuned at Newport with the specified load in place. Narrow band techniques add less weight than competitive "dry dampers" that can actually increase vibration problems by placing more load at the table ends and decreasing the stiffness-to-weight ratio. Dry dampers incorporate semi-rigid adhesive layers which can degrade over time. As a result, dry dampers are not as reliable as the low vapor pressure, hermetically sealed oil damping techniques used by Newport.
Yes, if properly applied. All figures of merit; such as the Maximum Relative Motion and Dynamic Deflection Coefficient; are extracted from a combination of measured data and assumptions. The methods of calculation and assumptions should be clearly stated by the manufacturer or the data may not be comparable. Newport uses these figures of merit conservatively for the benefit of its customers when comparing among the many tables offered by Newport. Manufacturer data claiming maximum compliance levels and maximum static deflection should be discarded unless the computational method is clearly stated. In any case, the best evaluation is the direct comparison of compliance curves measured at the proper table location.
The most important data shown on compliance curves are the table resonance frequencies and the "Q" of each resonance. Higher resonance frequencies result in lower table deflection. Minimum "Q"; the ratio of peak compliance to the ideal rigid body compliance at the same frequency; indicates high table damping and reduced bending due to vibration.
Yes. Newport offers two types of side walls: wood composite for laboratory use and damped metal sides for cleanroom and vacuum applications. The wood sides are acoustically superior to any competitor's metal sides - tap on them and you can hear the difference! The composite wood will not corrode and is epoxy sealed against liquid contaminants.
Freestanding legs offer better isolation than legs coupled together with tie-bars. Tie-bar systems can introduce vibration modes directly into the leg. They also offer a false sense of security in earthquake zones. Tie-bars should only be used if rolling casters are required. In earthquake zones, approved Newport earthquake restraints should be used.
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