Collimators are used to change the size of the laser beam. They are also known as beam expanders or up-collimators when they are used to increase the size of the beam. Beam collimation is useful for creating a desired laser spot size, or for controlling the beam diameter over long distances (larger beam diameters display lower beam divergence). Collimators can be transmissive (using lenses) or reflective (using mirrors). A transmissive collimator (also known as a beam telescope or a Galilean telescope) is a relatively simple device using a combination of a negative lens and a positive lens. Reflective collimators are used with higher power lasers because of the potential thermal effect on transmissive lenses at these higher powers. Various expansion ratios, input apertures and mounting configurations are available.
