The collimating lens captures the highly divergent output from the optical fiber and creates a parallel (collimated) beam with reduced divergence enabling moderate propagation distances.

Collimating lenses, as well as focusing lenses present in fiber laser cutting heads, are very sensitive to any type of contamination. For this reason, the majority of fiber laser systems employ protective windows to protect the focusing lens against contamination. Collimating lenses, as well as focusing lenses present in fiber laser cutting heads, are very sensitive to any type of contamination. For this reason, the majority of fiber laser systems employ protective windows to protect the focusing lens against contamination. The protective window is positioned in front of the focusing lens and serves as a barrier between the lens and the metal sheet.