Design of Refractive, High-NA, Freeform Beam Shaping Systems

High-NA beam shaping systems can be used for the generation of narrow light distributions (for example Top Hats). The beam shaping can be done by a paraxial beam shaping element combined with high-NA lens system or by a single high-NA beam shaping element. For the optimization of single high-NA refractive beam shaping elements iterative and parametric optimization techniques were suggested. Published optimization techniques are often based on a geometrical optics modeling of light propagation or can just optimize rotational symmetric surfaces. The authors show extensions of parametric and iterative optimization techniques that allow the optimization of high-NA freeform refractive beam shaping elements including diffraction and interference effects. The optimization is demonstrated on the example of the reshaping of a Gaussian laser beam into a rectangular Top Hat by a beam shaping system with an NA of 0.7 using the optical design software VirtualLab. The optimization results of parametric and iterative techniques are compared. Differences between scalar and vectorial modeling are discussed.