Speaker
Description
KAOS (Kirkpatrick–Baez Active Optical System) has been a long-standing companion of the FERMI Free Electron Laser and, more broadly, of the XEUV community, evolving together with the scientific questions it was meant to address. Conceived, developed and continuously refined within PADReS, KAOS was initially designed as an adaptive optical system aimed at achieving—and preserving—the best possible focus at the sample.
Over time, however, its role expanded beyond focal optimization. KAOS progressively became a versatile platform for beam shaping, enabling controlled illumination conditions tailored to different experiments. These include deliberately defocused configurations with decoupled focal dimensions, integration with diffractive optics such as Fresnel zone plates, and the extension toward non-conventional illumination schemes including beams carrying orbital angular momentum (OAM). Such capabilities have supported a broad range of techniques, from pump–probe spectroscopy and coherent diffraction imaging to nano-spectroscopy, nonlinear FEL experiments, interferometry, and structured illumination with vortex beams.
Throughout this evolution, wavefront sensing has played a central role. If KAOS were a sports car, wavefront sensing would be its pilot. Initially introduced to optimize mirror alignment and optical performance, it progressively became a key element for advanced beam shaping, evolving from a tool for tuning the optics to a direct diagnostic of the wavefront itself. A recent example is the characterization of OAM beams used by FERMI scientists and collaborators to explore new opto-magnetic interactions.
This contribution briefly revisits the experience accumulated with KAOS—not only to summarize what has been achieved, but also to stimulate new ideas. If the past showed what active wavefront control can do, the next question is simple: what could the next generation do with it?