A beam expander is a two or more element optical system that changes the beam’s size and divergence characteristics. Beam expanders have numerous uses. By expanding a beam prior to focusing, smaller focal spot sizes can be achieved. Beam expanders improve a beam’s collimation. They are also used to reduce the beam diameter which may be useful when using acousto- or electro-optic modulators. Using a spatial filter with a beam expander can make an asymmetrical beam profile more symmetric and provide more uniform energy distribution
