The focusing lens is the last optic in the laser path, before it hits the workpiece. Its main role is to focus the laser beam to a specific focal length (FL) - depending on the application. Therefore, the focal length - that is dictated by the radiuses and curvatures of the lens - is its most important feature.

Focal length (FL) refers to the distance from the laser focusing lens to the top surface of the material being processed, which is often measured in inches. On the other hand, focus refers to the smallest possible beam of a laser. And this beam has the maximum density of laser packed in it.