A beam expander is an optical system for changing the beams diameter. The product of the diameter and divergence for a laser beam remains constant between input and output. This means that, if the beam diameter increases, the divergence of the output will decrease. Beam expanders use this inverse-proportional relationship between the diameter and divergence to expand a laser beam, or to reduce the beam divergence. Low divergence allows for a smaller focus spot of a Gaussian beam. In summary, beam expanders are used for fine focusing, reducing beam divergence and minimizing diffraction effect. Daheng Beam Expanders (GCO-14) are professionally designed for complicated systems and ideally used in combination with Daheng F-Theta lenses (GCO-31).