In this work, we exploit HHG in a noble gas to merge the azimuthally twisted wavefront of a vortex beam and the spatially varying polarization of a vector beam, yielding EUV vector-vortex beams (VVB) that are tailored simultaneously in their SAM and OAM. Employing a high-resolution EUV Hartmann wavefront sensor (EUV HASO, Imagine Optic), we perform the complete spatial intensity and wavefront characterization of the vertical polarization component of the 25th harmonic beam centered at a wavelength of 32.6 nm. By driving the HHG using IR VVB, we show that HHG enables the production of EUV VVB exhibiting radial, azimuthal, or even intermediate polarization distribution. Furthermore, the wavefront characterization allows for the unambiguous confirmation of the topological charge and OAM helicity of the upconverted harmonic VVB. Notably, our work reveals that HHG provides a means for the synchronous and controlled manipulation of SAM and OAM. The production of ultrafast EUV VVB with high OAM and adjustable polarization distributions opens up promising prospects for their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source.
High-order harmonic generation (HHG) is an instrumental process enabling the transfer of short infrared pulse coherence properties into the Extreme Ultraviolet (EUV) spectral range. This phenomenon has opened the way to ultrafast pump-probe experiments at the nanoscale level. Recently, HHG has provided a straightforward approach to frequency upconvert beams structured in their phase and/or polarization. An emblematic example is the optical vortex beam, which is characterized by an azimuthally twisting wavefront. From a fundamental point of view, such a beam exhibits a phase singularity on the propagation axis and is carrying orbital angular momentum (OAM). Vector beams denote another structured beam family, exhibiting a spatially varying polarization.
In this paper, we will present our recent results on the generation and characterization of EUV vortex beams exhibiting very high topological charges (up to 100). Besides, using a similar HHG up-conversion scheme, we will show the production of so-called EUV vector-vortex beams that present the combined characteristics of the vortex and vector beams. Finally, progress on plasma-based soft x-ray laser amplification of such structured beams will be outlined,
We report on the development and implementation of a diagnostic for the temporal characterization of seeded XUV laser pulses, based on laser-dressed photoionization in the sideband regime, using a home-made velocity map-imaging spectrometer as the central element. The diagnostic was recently tested at the LASERIX facility with the seeded Ne-like titanium laser at 38 eV as the XUV source, overlapped with an infrared pulse of variable duration and intensity.
We report temporal coherence measurement of solid-target plasma-based soft X-ray laser (XRL) in amplified spontaneous emission (ASE) mode. By changing the XRL pumping angle, we generate lasing at two-times higher electron density than the routine condition. A relatively shorter coherence time at a higher pumping angle indicates a clear spectral signature of higher electron density in the gain region. We probe the amplification dynamics of XRL in routine, and high electron density conditions to confirm gain-duration reduction resulting from ionization gating in the latter case. We also present recent results on the seeding of a vortex beam carrying orbital angular momentum (OAM) in XRL plasma. A small part of the high topological charge extreme ultraviolet (EUV) vortex is injected in XRL. These preliminary results suggest that the vortex seed indeed can be efficiently amplified. In the end, we propose a pathway towards the seeding of the complete vortex beam and wavefront characterization of the amplified beam.
We present an experimental intensity and wavefront characterization of the infrared vortex driver as well as the extreme ultraviolet vortex obtained through high harmonic generation in an extended generation medium. In a loose focusing geometry, an intense vortex beam obtained through phase-matched absorption-limited high harmonic generation in a 15 mm long Argon filled gas-cell permits single-shot characterization of the vortex structure. Moreover, our study validates the multiplicative law of momentum conservation even for such an extended generation medium.
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