Bright, High-Frequency, Circularly Polarized Structured Attosecond Pulses

The generation of circularly polarized (CP) attosecond pulses is demanding and complicated to achieve, especially in the x-rays where standard polarization converters are highly inefficient. During the last decade, sophisticated configurations of high harmonic generation (HHG) have provided different alternatives to generate CP high-order harmonics in the extreme ultraviolet regime [1], [2]. Among these techniques, only the use of a noncollinear scheme [3] has been able to spatially separate CP high-order harmonics with the same helicity, and thus to provide CP attosecond pulses [4]. Such scheme is based on producing a “rotating polarization grating” along the transverse coordinate across the driving laser focus. However, the efficient interaction region is limited by the noncollinear angle, which further limits the overall conversion efficiency of the process.