Beam expander

laser

A laser beam expander is designed to either decrease the laser's beam spot size at large distances or produce a larger collimated output laser beam. Laser beam expanders come in two main types: Keplerian laser beam expander or a Galilean laser beam expander. In its simplest form a Galilean beam expander consists of a postive and a negative focal length lens whereas the Keplerian consists of two postive focal length lenses. More advanced forms of laser beam expander utilise more than two lens elements to correct for spherical abberation. Both beam expander designs provide a certain anular magnifaction, called expander power. The beam diameter is first increased in size by this power and then the beam divergence is reduced by the same power. This combination yields a beam that is not only larger, but one that is highly collimated. The result is a smaller beam at large distances when compared to the laser alone. The laser beam expander is also useful when a larger collimated beam is required over a given range.