Speaker
Description
The quest of achieving complete control over the generation of coherent x-ray sources has driven the efforts over the scientific community during the last years due to their unique ability to capture the fastest electronic and spin dynamics in a wide variety of materials. Among other x-ray sources, high-harmonic generation (HHG) stands as a robust mechanism to generate highly spatially and temporally coherent radiation from the extreme-ultraviolet (EUV) to the soft x-ray regimes, with exquisite temporal accuracy in the attosecond regime. Remarkably, such control is acquired through a highly nonlinear up-conversion process, where the properties of an infrared driving field are mapped into high-frequency harmonics. However, such mapping process is far from trivial.
In this contribution we will review the recent advances in the generation of structured coherent EUV/soft x-ray pulses through HHG. In particular, the use of structured driving beams with controlled spin and/or orbital angular momentum has opened exciting opportunities to harness the properties of the high-order harmonics and attosecond pulses [1], such as their polarization state [2-5], their self-torque [6], or their spectral and focusing properties [7].
References
[1] C. Hernández-García, “A twist in coherent X-rays”, Nature Physics 13, 327-329 (2017).
[2] P.-C. Huang, et al., “Polarization Control of Isolated High-Harmonic Pulses”, Nature Photonics 12, 349-354 (2018).
[3] K.-Y. Chang, et al. “High-Order Nonlinear Dipole Response Characterized by Extreme-Ultraviolet Ellipsometry”, Optica 8, 484 (2021).
[4] K. M. Dorney, et al. “Controlling the polarization and vortex charge of attosecond high-harmonic beams via simultaneous spin-orbit momentum conservation”. Nat. Photon. 13, 123-130 (2019).
[5] L. Rego, J. San Román, L. Plaja, C. Hernández-García, “Trains of attosecond pulses structured with time-ordered polarization states”, Opt. Lett. 45, 5636-5639 (2020).
[6] L. Rego, et al., “Generation of extreme-ultraviolet beams with time-varying orbital angular momentum”. Science 364, eaaw9486 (2019).
[7] L. Rego et al. “Necklace-structured high harmonic generation for low-divergence, soft X-ray harmonic combs with tunable line spacing”, under review.
About the speaker:
Dr. Carlos Hernández-García (36) is a Senior Researcher (Ramón y Cajal Fellow), at Universidad de Salamanca (Spain). PI of the ERC Starting Grant project ATTOSTRUCTURA. More than 50 peer-review articles indexed in JCR (including 3 Science, 3 Nature Photonics, 2 PNAS, 5 PRL, 3 Optica, among others). Recipient of the 2019 Fresnel Prize, awarded by the European Physical Society (EPS) and the RSEF-BBVA Physics Prize 2019 for Young Researchers, awarded by the Royal Spanish Society and the BBVA Foundation.
