Beam Expander Calculator
Calculate lens focal lengths, system length, output beam diameter, and divergence for Keplerian and Galilean beam expander configurations.
A beam expander increases beam diameter by a factor M while reducing divergence by 1/M, using a pair of lenses separated by the sum of their focal lengths. Two configurations exist: Keplerian (positive–positive lens pair, real intermediate focus) and Galilean (negative–positive, no intermediate focus, more compact). This calculator determines both lens focal lengths, the physical system length, and the output beam diameter and divergence for a given expansion ratio and input beam. Use this tool when coupling to spatial filters, reducing laser beam divergence for long propagation paths, or increasing beam diameter to fill a large aperture.
Note: The Keplerian configuration has an internal focal point between the lenses, suitable for spatial filtering with a pinhole. Avoid with high-power pulsed lasers due to air breakdown risk at focus.