What is it about?
Recent advances in physics have often been made possible by cutting-edge technology. In the fields of photonics and X-ray science, this means developing new ways to control the properties of light beams. At the FERMI Free-Electron Laser facility in Trieste, Italy, OAM beams are created by either modifying the emission process or, more commonly, by using a spiral zone plate (SZP) combined with the Kirkpatrick–Baez active optic system (KAOS), which helps to focus and shape the beam. To ensure a consistent and reliable setup for users, a Hartmann wavefront sensor (WFS) is used to fine-tune the optics and measure the beam's characteristics. KAOS can produce both tightly focused and broader beams, with separate control over vertical and horizontal magnification. This study explores a new, less conventional method called ‘near collimation’ to generate OAM beams. This method uses a specially designed SZP to achieve the desired results. The article examines the performance of the mirrors using Hartmann wavefront sensing, discusses different methods for analyzing the data, and provides a detailed analysis of these results using a technique called ptychographic reconstruction.
Why is it important?
Orbital angular momentum (OAM) beams hold substantial promise in various domains such as ultra-high-capacity optical communication, rotating body detection, optical tweezers, laser processing, super-resolution imaging etc. Hence, the advancement of OAM beam-generation technology and the enhancement of its technical proficiency and characterization capabilities are of paramount importance.