Beam Expander

A beam expander is any optical system designed to increase the diameter of a laser beam. In most cases, the term is taken to mean a telescope designed to take a small-diameter collimated beam input beam and produce a larger diameter collimated output beam, thus reducing the divergence of the beam. The beam expander consists of a negative input lens and a positive objective. The expansion factor is the ratio of the focal length of the two lenses.