Search

[EN]High-harmonic generation (HHG) is a unique tabletop light source with femtosecond-to-attosecond pulse duration and tailorable polarization and beam shape. Here, we use counter-rotating femtosecond laser pulses of 0.8 µm and 2.0 μm to extend the photon energy range of circularly polarized high-harmonics and also generate single-helicity HHG spectra. By driving HHG in helium, we produce circularly polarized soft x-ray harmonics beyond 170 eV—the highest photon energy of circularly polarized HHG achieved to date. In an Ar medium, dense spectra at photon energies well beyond the Cooper minimum are generated, with regions composed of a single helicity—consistent with the generation of a train of circularly polarized attosecond pulses. Finally, we show theoretically that circularly polarized HHG photon energies can extend beyond the carbon K edge, extending the range of molecular and materials systems that can be accessed using dynamic HHG chiral spectro-microscopies, Department of Energy BES (DE-FG02-99ER14982); Air Force Office of Scientific Research (FA9550-16-1-0121); National Science Foundation (DGE-1144083, DGE-1650115); European Research Council (8511201); Ministerio de Ciencia, Innovación y Universidades (PID2019-106910GB-100); Junta de Castilla y León (SA287P18); Ramón y Cajal contract (RYC-2017-22745).

[EN]Optical interactions are governed by both spin and angular momentum conservation laws, which serve as a tool for controlling light–matter interactions or elucidating electron dynamics and structure of complex systems. Here, we uncover a form of simultaneous spin and orbital angular momentum conservation and show, theoretically and experimentally, that this phenomenon allows for unprecedented control over the divergence and polarization of extreme-ultraviolet vortex beams. High harmonics with spin and orbital angular momenta are produced, opening a novel regime of angular momentum conservation that allows for manipulation of the polarization of attosecond pulses—from linear to circular—and for the generation of circularly polarized vortices with tailored orbital angular momentum, including harmonic vortices with the same topological charge as the driving laser beam. Our work paves the way to ultrafast studies of chiral systems using high-harmonic beams with designer spin and orbital angular momentum., The authors are thankful for useful and productive conversations with E. Pisanty, C. Durfee, D. Hickstein, S. Alperin and M. Siemens. H.C.K. and M.M.M. graciously acknowledge support from the Department of Energy BES Award No. DE-FG02–99ER14982 for the experimental implementation, as well as a MURI grant from the Air Force Office of Scientific Research under Award No. FA9550–16–1–0121 for the theory. J.L.E., N.J.B. and Q.L.N. acknowledge support from National Science Foundation Graduate Research Fellowships (Grant No. DGE-1144083). C.H.-G., J.S.R. and L.P. acknowledge support from Junta de Castilla y León (SA046U16) and Ministerio de Economía y Competitividad (FIS2013–44174-P, FIS2016–75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. L.R. acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). A.P. acknowledges support from the Marie Sklodowska-Curie Grant, Agreement No. 702565. We thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (RES-AECT-2014–2–0085). This research made use of the high-performance computingresources of the Castilla y León Supercomputing Center (SCAYLE, www.scayle.es),financed by the European Regional Development Fund (ERDF). Certain commercial instruments are identified to specify the experimental study adequately. This does not imply endorsement by the National Institute of Standards and Technology (NIST) or that the instruments are the best available for the purpose.

Optical interactions are governed by both spin and angular momentum conservation laws, which serve as a tool for controlling light–matter interactions or elucidating electron dynamics and structure of complex systems. Here, we uncover a form of simultaneous spin and orbital angular momentum conservation and show, theoretically and experimentally, that this phenomenon allows for unprecedented control over the divergence and polarization of extreme-ultraviolet vortex beams. High harmonics with spin and orbital angular momenta are produced, opening a novel regime of angular momentum conservation that allows for manipulation of the polarization of attosecond pulses—from linear to circular—and for the generation of circularly polarized vortices with tailored orbital angular momentum, including harmonic vortices with the same topological charge as the driving laser beam. Our work paves the way to ultrafast studies of chiral systems using high-harmonic beams with designer spin and orbital angular momentum.

Light beams carrying orbital angular momentum (OAM) [1] are well known due to their powerful capabilities for applications in many fields, such as optical communications, microscopy, quantum optics, quantum information or microparticle manipulation [2]. In this work we introduce a new class of light beams that possess a unique property associated with a temporal variation of their OAM: the self-torque of light [3]. Despite the recent progress in the generation of designer ultrafast light waveforms with OAM [4–6], up to now there is no evidence for the creation of pulses with time-dependent OAM in any spectral regime. We define the self-torque of light as ħξ = ħdl(t)/dt, where ħl(t) represents the inherent time-variation of a beam's OAM. This definition has an analogy with mechanical systems that self-induce a variation of their angular momentum.

The angular momentum of light is present in two different forms: spin angular momentum (SAM), related to the field's polarization, and orbital angular momentum (OAM), associated with the spatial profile of the phase of the electromagnetic wave. While these properties have been long studied and exploited in the visible/infrared regions, recent developments have extended SAM [1,2] and OAM [3,4] control into the EUV/soft x-ray regions. However, to date it has not been possible to generate coherent EUV beams with fully controlled SAM and OAM.

High-order harmonic generation stands as a unique nonlinear optical up-conversion process, mediated by a laser-driven electron recollision mechanism, which has been shown to conserve energy, linear momentum, and spin and orbital angular momentum. Here, we present theoretical simulations that demonstrate that this process also conserves a mixture of the latter, the torus-knot angular momentum Jγ, by producing high-order harmonics with driving pulses that are invariant under coordinated rotations. We demonstrate that the charge Jγ of the emitted harmonics scales linearly with the harmonic order, and that this conservation law is imprinted onto the polarization distribution of the emitted spiral of attosecond pulses. We also demonstrate how the nonperturbative physics of high-order harmonic generation affect the torus-knot angular momentum of the harmonics, and we show that this configuration harnesses the spin selection rules to channel the full yield of each harmonic into a single mode of controllable orbital angular momentum., We thank T. Ruchon for helpful observations. E. P. acknowledges Cellex-ICFO-MPQ fellowship funding; E. P. and M. L. acknowledge the Spanish Ministry MINECO (National Plan 15 Grants: FISICATEAMO No. FIS2016-79508-P, SEVERO OCHOA No. SEV-2015-0522, FPI), European Social Fund, Fundació Cellex, Generalitat de Catalunya (AGAUR Grant No. 2017 SGR1341 and CERCA/Program), ERC AdG OSYRIS, EU FETPRO QUIC, and the National Science Centre, Poland-Symfonia Grant No. 2016/20/W/ST4/00314. A. P. acknowledges funding from Comunidad de Madrid through TALENTO Grant No. 2017-T1/IND-5432. J. S. R., L. P., and C. H.-G acknowledge support from Junta de Castilla y León (SA046U16) and Ministerio de Economía y Competitividad (FIS2013-44174-P, FIS2016-75652-P). C. H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation and Ministerio de Ciencia, Innovación y Universidades for a Ramón y Cajal contract (RYC-2017-22745), co-funded by the European Social Fund. L. R. acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). H. C. K. and M.M.M. acknowledge support from the Department of Energy BESAwardNo.DE-FG02–99ER14982, as well as aDARPATEE Award No. D18AC00017. We thankfully acknowledge thecomputer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (RES-AECT-2014-2-0085). This research made use of the high-performance computing resources of the Castilla yLeón Supercomputing Center (SCAYLE), financed by the European Regional Development Fund (ERDF).

Extreme-ultraviolet, attosecond beams with custom spin and orbital angular momentum are produced via high-harmonic generation, for the first time. Entwined angular momentum conservation rules yield exquisite control over their polarization, divergence, and vortex charge.

Light fields carrying orbital angular momentum (OAM) provide powerful capabilities for applications in optical communications, microscopy, quantum optics, and microparticle manipulation. We introduce a property of light beams, manifested as a temporal OAM variation along a pulse: the self-torque of light. Although self-torque is found in diverse physical systems (i.e., electrodynamics and general relativity), it was not realized that light could possess such a property. We demonstrate that extreme-ultraviolet self-torqued beams arise in high-harmonic generation driven by time-delayed pulses with different OAM. We monitor the self-torque of extreme-ultraviolet beams through their azimuthal frequency chirp. This class of dynamic-OAM beams provides the ability for controlling magnetic, topological, and quantum excitations and for manipulating molecules and nanostructures on their natural time and length scales., C.H.-G., J.S.R., and L.P. acknowledge support from Junta de Castilla y León (SA046U16), Ministerio de Economía y Competitividad (FIS2016-75652-P), FEDER funds, and Ministerio de Ciencia, Innovación y Universidades (Eq. C2018-0041 17-P). L.R. acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation, and Ministerio de Ciencia, Innovación y Universidades for a Ramón y Cajal contract (RYC-2017-22745), cofunded by the European Social Fund. H.K. and M.M. acknowledge support from the Department of Energy BES Award no. DE-FG02-99ER14982 for the experimental implementation, the DARPA TEE Program Award. no. D18AC00017 for the new experimental characterization methods developed, as well as a MURI grant from the Air Force Office of Scientific Research under Award no. FA9550-16-1-0121 for the theory. Q.L.N. acknowledges support from National Science Foundation Graduate Research Fellowships (grant no. DGE-1144083). N.J.B. and D.C. acknowledge support from National Science Foundation Graduate Research Fellowships (grant no. DGE-1650115). E.P. acknowledges Cellex-ICFOMPQ fellowship funding; E.P. and M.L. acknowledge the Spanish Ministry MINECO (National Plan 15 Grant: FISICATEAMO no. FIS2016-79508-P, SEVERO OCHOA no. SEV-2015-0522, FPI), European Social Fund, Fundaci Cellex, Generalitat de Catalunya (AGAUR grant no. 2017 SGR 1341 and CERCA/Program), ERC AdG OSYRIS, EU FETPRO QUIC, and the National Science Centre, Poland-Symfonia grant no. 2016/20/W/ST4/00314. We acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (RES-AECT-2014-2-0085). This research made use of the high-performance computing resources of the Castilla y León Supercomputing Center (SCAYLE, www.scayle.es/), financed by the European Regional Development Fund (ERDF).

We present high-resolution, simultaneous two-color phase-and-amplitude characterization of 2nd harmonic up-conversion in OAM beams by ptychography. We measure topological charge conservation during 2nd harmonic generation process, which can be extended to high-order harmonic upconversion.

We experimentally demonstrate straightforward methodologies for generating high harmonics of arbitrary polarization state. Polarization control is realized by adjusting the intensity ratio of the bicircular driving field or by exploiting chirally dependent Cooper minima transitions.

We present a method of producing ultrashort pulses of circularly polarized extreme ultraviolet (EUV) light through high-harmonic generation (HHG). HHG is a powerful tool for generating bright laser-like beams of EUV and soft x-ray light with ultrashort pulse durations, which are important for many spectroscopic and imaging applications in the materials, chemical, and nano sciences. Historically HHG was restricted to linear polarization; however, recent advances are making it possible to precisely control the polarization state of the emitted light simply by adjusting the driving laser beams and geometry. In this work, we gain polarization control by combining two spatially separated and orthogonally linearly polarized HHG sources to produce a far-field beam with a uniform intensity distribution, but with a spatially varying ellipticity that ranges from linearly to fully circularly polarized. This spatially varying ellipticity was characterized using EUV magnetic circular dichroism, which demonstrates that a high degree of circularity is achieved, reaching almost 100% near the magnetic M-edge of cobalt. The spatial modulation of the polarization facilitates measurements of circular dichroism, enabling us to measure spectrally resolved magnetic circular dichroism without the use of an EUV spectrometer, thereby avoiding the associated losses in both flux and spatial resolution, which could enable hyperspectral imaging of chiral systems. Through numerical simulations, we also show the generality of this scheme, which can be applied with either the discrete harmonic orders generated by many-cycle pulses or the high-harmonic supercontinua generated by few-cycle driving laser pulses. Therefore, this technique provides a promising route for the production of bright isolated attosecond pulses with circular polarization that can probe ultrafast spin dynamics in materials., U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES) (DE-FG02-99ER14982, DE-SC0002002); National Science Foundation (NSF) (DGE-1144083); Fundación BBVA; Ministerio de Economía y Competitividad (MINECO) (FIS2016-75652-P); Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO); Barcelona Supercomputing Center - Centro Nacional de Supercomputación (BSC-CSN) (RES-FI-2017-3-0004).

We generate angularly isolated beams of circularly polarized extreme ultraviolet light through the first implementation of non-collinear high harmonic generation with circularly polarized driving lasers. This non-collinear technique offers numerous advantages over previous methods, including the generation of higher photon energies, the separation of the harmonics from the pump beam, the production of both left and right circularly polarized harmonics at the same wavelength and the capability of separating the harmonics without using a spectrometer. To confirm the circular polarization of the beams and to demonstrate the practicality of this new light source, we measure the magnetic circular dichroism of a 20 nm iron film. Furthermore, we explain the mechanisms of non-collinear high harmonic generation using analytical descriptions in both the photon and wave models. Advanced numerical simulations indicate that this non-collinear mixing enables the generation of isolated attosecond pulses with circular polarization., This work was completed at JILA. D.H., J.E., T.F., K.D., H.C. and M.M. acknowledge support from the Department of Energy BES Award DE-FG02-99ER14982. M.M., H.K. and C.D. acknowledge support from the National Science Foundation’s Engineering Research Centre in Extreme Ultraviolet Science and Technology. C.D. acknowledges support from the Air Force Office of Scientific Research under MURI grant FA9550-10-1-0561. J.E. acknowledges support from the National Science Foundation Graduate Research Fellowship (DGE-1144083). C.H.-G. acknowledges support from a Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007–2013), under REA grant agreement no. 328334. C. H.-G. acknowledges support from Junta de Castilla y León (Project SA116U13) and MINECO (FIS2013-44174-P). A.J.-B. was supported by grants from the National Science Foundation (grants nos. PHY-1125844 and PHY-1068706). This work made use of the Janus supercomputer, which is supported by the National Science Foundation (award no. CNS-0821794) and the University of Colorado, Boulder. P.G. acknowledges support from the Deutsche Forschungsgemeinschaft (grant no. GR 4234/1–1). R.K. acknowledges the Swedish Research Council (VR) for financial support. A.B. acknowledges support from the Department of Energy, Office of Basic Sciences.

The increased worldwide exploitation of nanomaterials has reinforced the importance of introducing nanoscale aspects into the undergraduate and graduate curriculum. To meet this need, a novel nano-laboratory module was developed and successfully performed by science and engineering students. The main goal of the experiment was to accurately quantify the total silver composition of a nanocolloid with modern inductively coupled plasma–optical emission spectroscopy (ICP-OES) instrumentation in conjunction with two well-established methods that are heavily employed in both research and industrial settings. Specifically, undergraduate and graduate students estimated the total silver composition of Creighton colloidal nanoparticles via the external calibration method (16.3 ± 4.7 mg L-1) and the standard addition method (14.9 ± 4.2 mg L-1) at two emission wavelengths (328.068 and 338.898 nm). The assessment of basic laboratory skills and the class assignments showed that the students successfully mastered the various aspects of sample/standard preparation, the operation of the ICP-OES instrument, and the data analysis. Students’ interest and experience in this laboratory were highly rated in the anonymous student evaluations.

When atoms are irradiated by two-color circularly polarized laser fields the resulting strong-field processes are dramatically different than when the same atoms are irradiated by a single-color ultrafast laser. For example, electrons can be driven in complex two-dimensional trajectories before rescattering or circularly polarized high harmonics can be generated, which was once thought impossible. Here, we show that two-color circularly polarized lasers also enable control over the ionization process itself and make a surprising finding: the ionization rate can be enhanced by up to $700%$ simply by switching the relative helicity of the two-color circularly polarized laser field. This enhancement is experimentally observed in helium, argon, and krypton over a wide range of intensity ratios of the two-color field. We use a combination of advanced quantum and fully classical calculations to explain this ionization enhancement as resulting in part due to the increased density of excited states available for resonance-enhanced ionization in counter-rotating fields compared with co-rotating fields. In the future, this effect could be used to probe the excited state manifold of complex molecules.

We report the development of a new three-dimensional (3D) momentum-imaging setup based on conventional velocity map imaging to achieve the coincidence measurement of photoelectrons and photo-ions. This setup uses only one imaging detector (microchannel plates (MCP)/phosphor screen) but the voltages on electrodes are pulsed to push both electrons and ions toward the same detector. The ion-electron coincidence is achieved using two cameras to capture images of ions and electrons separately. The time-of-flight of ions and electrons are read out from MCP using a digitizer. We demonstrate this new system by studying the dissociative single and double ionization of PENNA (2-phenylethyl-N,N-dimethylamine). We further show that the camera-based 3D imaging system can operate at 10 kHz repetition rate.

We investigate the macroscopic physics of noncollinear high harmonic generation (HHG) at high pressures. We make the first experimental demonstration of phase matching of noncollinear high-order-difference-frequency generation at ionization fractions above the critical ionization level, which normally sets an upper limit on the achievable cutoff photon energies. Additionally, we show that noncollinear high-order-sum-frequency generation requires much higher pressures for phase matching than single-beam HHG does, which mitigates the short interaction region in this geometry. We also dramatically increase the experimentally realized cutoff energy of noncollinear circularly polarized HHG, reaching photon energies of 90 eV. Finally, we achieve complete angular separation of high harmonic orders without the use of a spectrometer., Department of Energy BES Award DE-FG02-99ER14982. MURI grant from the Air Force Office of Scientific Research under Award Number FA9550-16-1-0121. National Science Foundation Graduate Research Fellowship (DGE-1144083). Junta de Castilla y León (Project SA046U16) and Spanish MINECO (FIS2013-44174-P, FIS2016-75652-P).

source of bright, circularly polarized, extreme ultraviolet, and soft x-ray beams, where the individual harmonics themselves are completely circularly polarized. Here, we demonstrate the ability to preferentially select either the right or left circularly polarized harmonics simply by adjusting the relative intensity ratio of the bichromatic circularly polarized driving laser field. In the frequency domain, this significantly enhances the harmonic orders that rotate in the same direction as the higher-intensity driving laser. In the time domain, this helicity-dependent enhancement corresponds to control over the polarization of the resulting attosecond waveforms. This helicity control enables the generation of circularly polarized high harmonics with a user-defined polarization of the underlying attosecond bursts. In the future, this technique should allow for the production of bright highly elliptical harmonic supercontinua as well as the generation of isolated elliptically polarized attosecond pulses., H. K. and M. M. graciously acknowledge support from the Department of Energy BES Award No. DE-FG02- 99ER14982 for the experimental implementation, as well as a MURI grant from the Air Force Office of Scientific Research under Award No. FA9550-16-1-0121 for the theory. J. E. and C. M. acknowledge support from National Science Foundation Graduate Research Fellowships (Grant No. DGE-1144083). C. H.-G. acknowl- edges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007-2013), under REA Grant No. 328334, from Junta de Castilla y León (Project No. SA046U16) and Spanish Ministerio de Economía y Competitividad, MINECO (Projects No. FIS2013-44174-P and No. FIS2016-75652-P). Part of this work utilized the Janus supercomputer, which is sup- ported by the U.S. National Science Foundation (Grant No. CNS-0821794) and the University of Colorado Boulder.

We experimentally investigate phase matching of high harmonic generation in a noncollinear geometry and demonstrate phase matching above critical ionization using noncollinear high-order-difference-frequency generation, which provides a route to maximize the generated photon energies.

Numerous nanoparticle (NP) fabrication methodologies employ “bottom-up” syntheses, which may result in heterogeneous mixtures of NPs or may require toxic capping agents to reduce NP polydispersity. Tangential flow filtration (TFF) is an alternative “green” technique for the purification, concentration, and size-selection of polydisperse NP suspensions or colloids, in that it allows for real-time analysis and reduces the usage of additional solvent and post-synthetic reagents. Upper-division undergraduate and graduate students in engineering and chemistry successfully applied a three-step TFF process to reduce the polydispersity of Creighton colloidal silver nanoparticles (AgNPs). UV–vis absorption spectroscopy in conjunction with the Lambert–Beer law and Mie’s solutions to the Maxwell equations were employed to rapidly estimate the concentration and size of nanosilver in each TFF-fractionated colloidal sample using the localized surface plasmon resonance (LSPR) of AgNPs. A thorough emphasis on “green” nan...

We experimentally demonstrate that ptychographic coherent diffractive imaging can be used to simultaneously characterize the amplitude and phase of bichromatic orbital angular momenta-shaped vortex beams, which consist of a fundamental field, together with its copropagating second-harmonic field. In contrast to most other orbital angular momentum characterization methods, this approach solves for the complex field of a hyperspectral beam. This technique can also be used to characterize other phase-structured illumination beams, and, in the future, will be able to be extended to other complex fields in the extreme ultraviolet or X-ray spectral regions, as well as to matter waves., The NSF STROBE STC (DMR-1548924); DOE BES AMOS grant (DE-FG02-99ER14982); the NSF GRFP (DGE 1650115); 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation; Junta de Castilla y León (SA046U16); Ministerio de Economía y Competitividad (FIS2016-75652-P).

Background/Aims: The quaternary benzo-phenanthridine alkaloid (QBA) chelerythrine (CET) is a pro-apoptotic drug and Na+/K+ pump (NKP) inhibitor in human lens epithelial cells (HLECs). In order to obtain further insight into the mechanism of NKP inhibition by CET, its sub-cellular distribution was quantified in cytosolic and membrane fractions of HLEC cultures by surface-enhanced Raman spectroscopy (SERS). Methods: Silver nanoparticles (AgNPs) prepared by the Creighton method were concentrated, and size-selected using a one-step tangential flow filtration approach. HLECs cultures were exposed to 50 μM CET in 300 mOsM phosphate-buffered NaCl for 30 min. A variety of cytosolic extracts, crude and purified membranes, prepared in lysing solutions in the presence and absence of a non-ionic detergent, were incubated with AgNPs and subjected to SERS analysis. Determinations of CET were based on a linear calibration plot of the integrated CET SERS intensity at its 659 cm-1 marker band as a function of CET concentration. Results: SERS detected chemically unaltered CET in both cytosol and plasma membrane fractions. Normalized for protein, the CET content was some 100 fold higher in the crude and purified plasma membrane fraction than in the soluble cytosolic extract. The total free CET concentration in the cytosol, free of membranes or containing detergent-solubilized membrane material, approached that of the incubation medium of HLECs. Conclusion: Given a negative membrane potential of HLECs the data suggest, but do not prove, that CET may traverse the plasma membrane as a positively charged monomer (CET+) accumulating near or above passive equilibrium distribution. These findings may contribute to a recently proposed hypothesis that CET binds to and inhibits the NKP through its cytosolic aspect.

Atoms undergoing strong-field ionization in two-color circularly polarized femtosecond laser fields exhibit unique two-dimensional photoelectron trajectories and can emit bright circularly polarized extreme ultraviolet and soft-x-ray beams. In this Letter, we present the first experimental observation of nonsequential double ionization in these tailored laser fields. Moreover, we can enhance or suppress nonsequential double ionization by changing the intensity ratio and helicity of the two driving laser fields to maximize or minimize high-energy electron-ion rescattering. Our experimental results are explained through classical simulations, which also provide insight into how to optimize the generation of circularly polarized high harmonic beams.

Strong-field ionization in two-color circularly polarized fields is studied, where both experimental measurements and theoretical analyses suggest that the production of high-energy electrons from electron-ion rescattering is optimized in counterrotating fields, and when the ponderomotive energies of the two laser fields are equal.

We present ultrafast photoemission measurements of isolated nanoparticles in vacuum using extreme ultraviolet (EUV) light produced through high harmonic generation. Surface-selective static EUV photoemission measurements were performed on nanoparticles with a wide array of compositions, ranging from ionic crystals to nanodroplets of organic material. We find that the total photoelectron yield varies greatly with nanoparticle composition and provides insight into material properties such as the electron mean free path and effective mass. Additionally, we conduct time-resolved photoelectron yield measurements of isolated oleylamine nanodroplets, observing that EUV photons can create solvated electrons in liquid nanodroplets. Using photoemission from a time-delayed 790 nm pulse, we observe that a solvated electron is produced in an excited state and subsequently relaxes to its ground state with a lifetime of 151 ± 31 fs. This work demonstrates that femotosecond EUV photoemission is a versatile surface-sensitive probe of the properties and ultrafast dynamics of isolated nanoparticles.

Ionization in intense two-color circularly polarized laser pulses is explored numerically and experimentally. Double ionization is enhanced with counterrotating fields, and diverse dynamics are uncovered that are impossible with linear polarization.

We present the first circularly polarized soft X-ray harmonics to photon energies >160eV. Bright phase matched beams are used to characterize important materials with intrinsic perpendicular magnetic anisotropy on tabletop for the first time

We use ultrafast extreme ultraviolet (EUV) light to conduct time-resolved photoemission measurements of isolated nanodroplets in vacuum. We observe the creation and relaxation of solvated electrons within the nanodroplets after the absorption of EUV photons.

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.

The lithium-sulfur (Li/S) concept has a theoretical specific capacity of 1672 mAh g−1based on the complete reduction of S into lithium sulfide (Li2S). Practically, however, a pure S electrode encounters low deliverable capacity and poor charge/discharge cycle life owing to S’s electrical insulation and problems associated with polysulfide dissolution. Here, we report our studies to couple S with reduced graphene oxide (rGO) prepared via either mechanical milling or chemical precipitation. The differences of the resulting rGO/S composites with respect to morphology, structure, composition, and phase transformations are extensively studied. Thermal analyses, X-ray diffraction, scanning electron microscopy, and Raman spectroscopic results on the chemical rGO/S consistently confirmed the existence of amorphous/nanocrystalline S and their homogeneous distribution as well as interaction with the rGO microstructure. The electrochemical performances of chemical rGO/S revealed a marked improvement in both capacity retention and S utilization compared to those of the mechanical rGO/S.

We present the first circularly-polarized soft X-ray harmonics to photon energies >160eV. Bright phase matched beams are used to characterize important materials with intrinsic perpendicular magnetic anisotropy for the first time using tabletop sources.

We present the first circularly polarized harmonics in the soft X-ray region and the physics underlying it. This source enables the first X-ray magnetic circular dichroism measurements in rare earth elements on tabletop.