A laser beam expander is a type of optical device commonly used in optical systems. Its main application purpose is to enlarge the beam diameter or compress the beam divergence angle. Refracting laser beam expanders evolved from telescopes and are often classified as either Galilean or Kepler-type. Both structures have their own advantages and disadvantages. Consequently, to adapt to different application requirements, the two forms of beam expander are modified, and optical devices for different application purposes, such as zoom beam expanders and achromatic beam expanders, are produced. The following is a case study of an achromatic beam expander.
