The final sources of vibration to consider are those instruments, components, and accessories that may impart vibrations directly on the table surface or in very close proximity to the application. In laboratory environments, air ducts, doorways, and machinery all can introduce acoustic noise that could impact beam stability, especially in free-space applications. Some additional sources of vibration, which are often overlooked by even the most veteran scientists and engineers, originate within the experiment themselves or from inconspicuous sources. Mechanical noise comes from a variety of sources. Building sway can also impact scanning-probe microscopy applications, as many probe tips are sensitive to low-frequency vibration.įigure 1. In most traditional laser applications, building sway has no impact on stability or results, but in some emerging applications in bioimaging, such as live-cell imaging, building sway can affect the ability to clearly image cells suspended in fluid. Figure 1 illustrates many common sources of facility noise and their typical frequency ranges. In some cases, machinery can be contained in acoustic housings to filter airborne noise as well.Įven foot traffic from nearby hallways can impact sensitive experiments, depending on the building construction and level of traffic. Machines also should be installed on soft mounts that attenuate vibration before it is transmitted to the floor. Machinery faults can be eliminated through redesign or maintenance. Common machinery problems include pump cavitation, unbalanced fans, and flow excitation of air-handling systems. The most common of these is mechanical equipment such as elevators, pumps, AC units, motors, compressors, and similar rotating equipment. More typical sources of facility vibrations are those that originate within the building itself and are either transmitted along the floor or move entire labs. Each of these could potentially excite additional resonances within structures or equipment that would lead to vibration or acoustic noise.
Another common ground-borne disturbance is vehicle traffic near buildings. Facilities along coastal areas can also be affected by tidal disturbances, depending on the magnitude of the waves and the sensitivity of the application. In most seismic events, safety takes priority over performance, and having equipment that is properly protected and restrained is essential. On one end of the spectrum are seismic events such as earthquakes, which impart both impulse and cyclic disturbances of potentially dangerous magnitude. Many potential sources of vibration within facilities can impact the results of precision processes or data collection. Work surfaces and optomechanical assemblies must be designed to reduce their response to any vibration transmitted through the isolation system. The third approach is maximizing the rigidity and damping characteristics of any optical support structures. The second is directly isolating the system from local ambient noise - isolation via distance from the disturbance or by using isolation products. The first is identifying the sources of vibration and implementing ways to eliminate or reduce their levels. In general, there are three common approaches to reducing mechanical excitation of photonic systems.