Design and performance of a refractive optical system that converts a Gaussian to a flattop beam

A system of two aspheric lenses is described, which efficiently converts a collimated Gaussian beam to a flattop beam. Departing from earlier designs, both aspheric surfaces were convex, simplifying their fabrication; the out put beam was designed with a continuous roll-off, allowing control of the f ar-field diffraction pattern; and diffraction from the entrance and exit ap ertures was held to a negligible level. The design principles are discussed in detail, and the performance of the as-built optics is compared quantita tively with the theoretical design. Approximately 78% of the incident power is enclosed in a region with 5% rms power variation. The 8-mm-diameter bea m propagates approximately 0.5 m without significant change in the intensit y profile; when the beam is expanded to 32 mm in diameter, this range incre ases to several meters. (C) 2000 Optical Society of America OCIS codes: 140 .3300, 220.1250, 220.2740.