Structured light in the short-wavelength regime opens exciting avenues for the study of ultrafast spin and electronic dynamics. Here, we demonstrate theoretically and experimentally the generation of vector-vortex beams (VVB) in the extreme ultraviolet through high-order harmonic generation (HHG). The up-conversion of VVB, which are spatially tailored in their spin and orbital angular momentum, is ruled by the conservation of the topological Pancharatnam charge in HHG. Despite the complex propagation of the driving beam, high-harmonic VVB are robustly generated with smooth propagation properties. Remarkably, we find out that the conversion efficiency of high-harmonic VVB increases with the driving topological charge. Our work opens the possibility to synthesize attosecond helical structures with spatially varying polarization, a unique tool to probe spatiotemporal dynamics in inhomogeneous media or polarization-dependent systems.
Recent
developments of high harmonic generation (HHG) have enabled
the production of structured extreme-ultraviolet (EUV) ultrafast laser
beams with orbital angular momentum (OAM). Precise manipulation and
characterization of their spatial structure are paramount for their
application in state-of-the-art ultrafast studies. In this work, we
report the generation and characterization of EUV vortex beams bearing
a topological charge as high as 100. Thanks to OAM conservation, HHG
in noble gases offers a unique opportunity to generate ultrafast harmonic
beams with a high topological charge from low charge infrared vortex
beams. A high-resolution Hartmann wavefront sensor allows us to perform
a complete spatial characterization of the amplitude and phase of
the 25th harmonic beam (32.6 nm), revealing very high-topological
charges in the EUV spectral regime. Our experimental results, supported
by numerical HHG simulations, demonstrate the linear upscaling of
the OAM of the high-order harmonics with that of low-charge driving
vortex beams, showing the sensitiveness of the OAM content to the
purity of the driving beam. The generation of structured EUV beams
carrying large topological charges brings in the promising scenario
of OAM transfer from light to matter at both macroscopic and microscopic
scales.
Unconscious perceptions and decisions are influenced by gender bias. In this work, we provide an exhaustive data analysis of the Ph.D. theses defended in the field of optics and photonics in Spain by filtering key descriptors and gender. Our results show a severe underrepresentation of women in the Ph.D. stage in the optics community, which becomes even more prominent in technological and theoretical domains. The gender gap is reduced in biomedical and visual optics. This asymmetry is a symptom of gender bias in science associated with traditional stereotypes about health and social care. Further studies and measures are required in specific areas of science to eradicate implicit gender-based associations in scientific disciplines.
Vigorous efforts to harness the topological properties of light have enabled a multitude of novel applications. Translating the applications of structured light to higher spatial and temporal resolutions mandates their controlled generation, manipulation, and thorough characterization in the short-wavelength regime. Here, we resort to high-order harmonic generation (HHG) in a noble gas to upconvert near-infrared (IR) vector, vortex, and vector-vortex driving beams that are tailored, respectively, in their spin angular momentum (SAM), orbital angular momentum (OAM), and simultaneously in their SAM and OAM. We show that HHG enables the controlled generation of extreme-ultraviolet (EUV) vector beams exhibiting various spatially dependent polarization distributions, or EUV vortex beams with a highly twisted phase. Moreover, we demonstrate the generation of EUV vector-vortex beams (VVB) bearing combined characteristics of vector and vortex beams. We rely on EUV wavefront sensing to unambiguously affirm the topological charge scaling of the HHG beams with the harmonic order. Interestingly, our work shows that HHG allows for a synchronous controlled manipulation of SAM and OAM. These EUV structured beams bring in the promising scenario of their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source.
The synchronous control of spin and orbital angular momentum in high-harmonic generation allows us to introduce experimentally and theoretically a novel XUV structured beam with spatially-varying polarization and phase, high topological charge, and robust propagation.
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