Flexible and robust beam shaping concepts with aspheres

Employing aspherical lenses to reduce aberrations to improve focusing qualities is a well-known concept. But the potpourri of aspherical surfaces offers way more possibilities, even the chance for flexible beam shaping setups. Since these are refractive optical elements the beam shaping is robust with respect to wavelength changes. Basic requirement for optimal and flexible usage of all beam shaping elements is a flexible beam expanding approach, which will be introduce as well. Being able to generate ring shaped light distributions is interesting for various applications. Here the most uncommon aspherical surface – an axicon – is utilized. Axicons are rotational symmetric prisms, which convert the incoming light into Bessel beams. Those are characterized by their concentrical ring structure and long depth of focus, which makes them very interesting for material processing. Above that, combining such an axicon with a focusing lens leads to a ring focus. Its size is not only determined by the choice of the axicon angle and the lens properties, but also through the diameter of the incoming beam. Thus, for optimal usage a flexible beam expander, which leaves the beam quality unaltered is mandatory. The remarkable properties of these beamshaping set-ups are shown in theory and experimentally.