Technical Note:
Stability of Optical Posts vs. Pedestals

The way you mount your optics can make the difference between a stable setup and one that suffers from vibrations. When building a setup, be sure to minimize beam height, use fewer parts (for instance, use a single post or pedestal rather than stacking them), and use parts made of thick, stiff material such as steel.

We offer two different mounting systems for your experiments— optical posts with post holders and pedestal risers. Posts with post holders are the more conventional alternative and are particularly convenient because they offer continuous height adjustment. Pedestals, on the other hand, offer significantly more stability because of their wider diameters, but are available only in fixed heights. For those in-between heights, try our Model 9950 pedestal shim set.

Posts vs. Pedestals

These two mounting systems react differently to forces such as vibrations or the force of your hand when making adjustments, which can affect your experiment. This motion becomes apparent during alignment of your optical system. The amount of motion caused by your hand during alignment is determined by the stiffness of the post or pedestal.

We designed our post holders with a lockable cam lever that distributes a large force evenly against the post. This gives you much better stability than conventional post holders that only lock with a screw. However, even this may not be stable enough for all applications.

As shown in the graph, the pedestal system shows much less deflection than a post for a given force, due to the pedestal’s larger diameter and increased stiffness. A stiff mounting system will make your optics easier to align, and will also perform better when excited by acoustic vibrations.

Added benefits of our pedestal system include a flange integrated onto the base and a relieved seat for extra-stable long-term mounting. Our fork system allows you to mount a pedestal anywhere on your optical table.

99-post vs pedestal
The deflection of a pedestal (shown in blue) is much less than the deflection of a post (shown in black) under an applied force.