Abstract

The study of light beams carrying integer orbital angular momentum (OAM) has become ubiquitous during the last two decades because of their unique capability to harness light matter-interaction with applications in different fields such as optical communications, super-resolution imaging, and quantum optics [1]. Alternatively, light beams carrying non-integer OAM have also recently been demonstrated. In particular, it has been demonstrated that half-integer OAM beams can be easily generated by means of conical refraction (CR) produced with optically biaxial crystals, with applications in optical trapping, free-space optical communications, material processing, and super-resolution imaging [2]. However, these applications are limited to the VIS-NIR domain due to the spectral bandwidth at which biaxial crystals are transparent (typically 400 nm–3000 nm). Therefore, new generation mechanisms of fractional-OAM beams at shorter wavelengths -such as the EUV and soft x-rays- are needed to extend the applicability of these techniques to the nanometer scale. High-order harmonic generation (HHG) stands as a unique frequency up-conversion process for the generation of coherent EUV and soft x-ray radiation, emitted in the form of attosecond bursts. A remarkable aspect of HHG is its natural ability to map the characteristics of the driving field to the high-frequency harmonics, this being fundamental in the generation of highly charged OAM beams in the EUV/x-ray domain [3-5].

© 2017 IEEE