OPTICAL SETUP
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Important Note: Optical components in the beam path must always be aligned to the actual beam
path, not the laser faceplate. Because of slight variations in laser construction, the beam path may
not always be centered in, or perpendicular to, the aperture in the faceplate.
Optical setup
After selecting a laser for a CO
2
laser processing system, the two most important elements to consider
are: (1) beam delivery optics to transmit the beam to the work area; and (2) focusing optics to focus the
beam onto the part or material to be processed. Each element is crucial in the development of a reliable
laser-based material processing system and each element should be approached with the same careful
attention to detail.
Beam delivery optics
Divergence, or expansion, of the laser beam is important in materials processing since a larger beam
entering the focusing optic produces a smaller focused spot.
Expander/collimators are optical devices that reduce beam divergence while at the same time increasing
beam diameter by a selectable magnification factor. Adding an expander/collimator substantially
reduces beam divergence and any variance in beam diameter caused by the changing optical path
length in an XY (“flying optics”) table application. In fixed-length delivery systems where the laser is
positioned only one meter away from the focusing optic and a small spot size is required, an
expander/collimator is again the best solution to provide the required beam expansion before reaching
the focusing optic.
Focusing optics
When selecting a focusing optic, the primary consideration should be material thickness and any vertical
tolerances that occur during final part positioning rather than selecting based only on minimum spot
size. The chosen focal length should create the smallest possible focused spot while providing the depth
of field required for the material to be processed.
Optics are fragile and must be handled carefully, preferably by the mounting ring only. Be careful to
select optics that are thick enough to withstand the maximum assist gas pressure available for the
process. This is especially important in metal cutting applications using high-pressure assist gases.
Cleanliness is another important issue affecting performance; a dirty or scratched lens will underperform
and exhibit a vastly shortened lifetime. When the laser application requires air as an assist gas, use only
breathing quality air available in cylinders from a welding supply company. Compressed shop air
contains minute particles of oil and other contaminants that will damage optical surfaces. If compressed
shop air is the only choice available, it must be filtered to the specifications shown in Table 4-1.
