Reflective beam expanders produce no central obscuration
A-1 Series reflective beam expanders have standard magnification configurations of 3.5x, 5x, 7.5x, 10x, and 30x, and magnify laser beams to 2 mm diameter. Unlike lens-based beam expanders, they can be used with collimated polychromatic light without needing fine focus adjustment. Manufactured to >λ/5 transmitted wavefront accuracies, they produce no central obscuration.
Optical Surfaces
Kenley, U.K.