Suchergebnisse

In this paper, we review the development and application of coherent short wavelength light sources implemented using the high harmonic generation (HHG) process. The physics underlying HHG brought quantum physics into the domain of attosecond time-scales for the first time. The observation and manipulation of electron dynamics on such short time-scales—a capability not conceived—of just a few decades ago—is becoming both more-and-more sophisticated and useful as a route to achieve exquisite control over short wavelength light. New experimental techniques are enabling HHG light sources to provide new insights into fundamental quantum interactions in materials, making it possible for the first time to capture the fastest charge, spin, photon and phonon interactions and to achieve diffraction-limited imaging at short wavelengths. ; We gratefully acknowledge support from the National Science Foundation through the JILA Physics Frontiers Center PHY-1734006, and a Gordon and Betty Moore Foundation EPiQS Award GBMF4538, for the attosecond ARPES setups and methods. We gratefully acknowledge support from the Department of Energy Office of Basic Energy Sciences XRay Scattering Program Award DE-SC0002002 for the spin dynamics setups and methods. We gratefully acknowledge support from the Department of EnergyOffice of Basic Energy Sciences AMOS Award DE-FG02-99ER14982 (experiment) as well as an MURI Grant from the Air Force Office of Scientific Research under Award Number FA9550-16-1-0121 (theory) for the HHG light source setups and methods. The authors gratefully acknowledge support from the STROBE National Science Foundation Science and Technology Center, Grant No. DMR-1548924, for the imaging setups and methods. C H-G acknowledges support by Ministerio de Ciencia, Innovación y Universidades for projects (FIS2016-75652-P and PID2019-106910GB-I00) and a Ramon y Cajal contract (RYC-2017-22745), co-funded by the European Social Fund; Junta de Castilla y León and European Union, FEDER, (Project SA287P18); and from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant agreement No. 851201). ZT gratefully acknowledges the financial support from the National Natural Science Foundation of China (Grant No.11874121), the Shanghai Municipal Science and Technology Basic Research Project (Grant No. 19JC1410900) and the Alexander-von-Humboldt foundation.

The extreme nonlinear optical process of high-harmonic generation (HHG) makes it possible to map the properties of a laser beam onto a radiating electron wave function and, in turn, onto the emitted x-ray light. Bright HHG beams typically emerge from a longitudinal phased distribution of atomic-scale quantum antennae. Here, we form a transverse necklace-shaped phased array of linearly polarized HHG emitters, where orbital angular momentum conservation allows us to tune the line spacing and divergence properties of extreme ultraviolet and soft x-ray high-harmonic combs. The on-axis HHG emission has extremely low divergence, well below that obtained when using Gaussian driving beams, which further decreases with harmonic order. This work provides a new degree of freedom for the design of harmonic combs—particularly in the soft x-ray regime, where very limited options are available. Such harmonic beams can enable more sensitive probes of the fastest correlated charge and spin dynamics in molecules, nanoparticles, and materials. ; The JILA team graciously acknowledges support from the Department of Energy BES Award No. DE-FG02-99ER14982 for the experimental implementation, a MURI grant from the Air Force Office of Scientific Research under Award No. FA9550-16-1-0121 for the mid-infrared laser soft x-ray research, and a National Science Foundation Physics Frontier Center grant PHY-1734006 for theory. N.J.B. acknowledges support from National Science FoundationGraduate Research Fellowships (grant no. DGE-1650115). Q.L.D.N. acknowledges support from National Science Foundation Graduate Research Fellowships (grant no. DGE-1144083). J.S.R., L.P., and C.H.-G. acknowledge support from Ministerio de Ciencia e Innovación (FIS2016-75652-Pand PID2019-106910GB-I00). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 851201). J.S.R., L.P., and C.H.-G. also acknowledge support from Junta de Castilla y León FEDER funds (project no. SA287P18). L.R. acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). C.H.-G. acknowledges Ministerio de Ciencia, Innovación, y Universidades for Ramón y Cajal contract (RYC-2017-22745), cofunded by the European Social Fund. L.R., J.S.R., L.P., and C.H.-G. thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (FI-2020-3-0013).

Bright, circularly polarized, extreme ultraviolet (EUV) and soft x-ray high-harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. Although the resulting circularly polarized harmonics consist of relatively simple pairs of peaks in the spectral domain, in the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency, and polarization. We extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with circularly polarized high-harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date. ; This work was done at JILA. We gratefully acknowledge support from the NSF through the Physics Frontiers Centers Program with grant no. PHY1125844 and the Gordon and Betty Moore Foundation EPiQS (Emergent Phenomena in Quantum Systems) Initiative through Grant GBMF4538 to M.M. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the European Union Seventh Framework Programme for Research and Technological Development (2007–2013), under Research Executive Agency grant agreement no. 328334. R.K. acknowledges the Swedish Research Council (VR) for financial support. A.J.-B. was supported by grants from the U.S. NSF (grant nos. PHY-1125844 and PHY-1068706). C.H.-G. and L.P. acknowledge support from Junta de Castilla y León (project SA116U13) and MINECO (Ministerio de Econom a y Competitividad) (FIS2013-44174-P and FIS2015-71933-REDT). This work used the Janus supercomputer, which is supported by the U.S. NSF (grant no. CNS-0821794) and the University of Colorado, Boulder. P.G. acknowledges support from the Deutsche Forschungsgemeinschaft (no. GR 4234/1-1).

We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. ; The authors thank Wilhelm Becker and Luis Plaja for useful discussions. Support for this work was provided by the Department of Energy (DOE) Office of Basic Energy Sciences X-Ray Scattering Program and the National Science Foundation (NSF) Physics Frontier Center Program Grant PHY-1125844 (to T.F., P.G., R.K., D.D.H., D.Z., C.G., F.J.D., C.A.M., C.W.H., J.L.E., K.M.D., C.C., T.P., A.B., H.C.K. and M.M.M.); NSF Graduate Research Fellowship DGE-1144083 (to J.L.E.); Marie Curie International Outgoing Fellowship within the European Union (EU) Seventh Framework Program for Research and Technological Development (2007–2013), under REA Grant 328334 (to C.H.-G.); Junta de Castilla y León Project SA116U13, UIC016 (to C.H.-G.); MINECO Grant FIS2013-44174-P (to C.H.-G.); US NSF Grants PHY- 1125844 and PHY-1068706 (to A.A.J.-B.); Deutsche Forschungsgemeinschaft Grant GR 4234/1-1 (to P.G.); Swedish Research Council (R.K. and P.M.O.); EU Seventh Framework Programme Grant 281043, FemtoSpin (to K.C. and P.M.O.); Czech Science Foundation Grant 15-08740Y (to K.C.); IT4Innovations Centre of Excellence Project CZ.1.05/1.1.00/02.0070 funded by the European Regional Development Fund and the national budget of the Czech Republic Project Large Research, Development and Innovations Infrastructures LM2011033 (to D.L.); US DOE, Office of Science, Office of Basic Energy Sciences Contract DE-SC0001805 (to O.G.S.); and US DOE Office of Basic Energy Sciences Award DE-SC0003678 (to E.E.F.). This work used the Janus supercomputer, which is supported by US NSF Award CNS-0821794 and the University of Colorado, Boulder.