Light-induced magnetization changes, such as all-optical switching, skyrmion nucleation, and intersite spin transfer, unfold on temporal and spatial scales down to femtoseconds and nanometers, respectively. Pump-probe spectroscopy and diffraction studies indicate that spatio-temporal dynamics may drastically affect the non-equilibrium magnetic evolution. Yet, direct real-space magnetic imaging on the relevant timescale has remained challenging. Here, we demonstrate ultrafast high-harmonic nanoscopy employing circularly polarized high-harmonic radiation for real-space imaging of femtosecond magnetization dynamics. We observe the reversible and irreversible evolution of nanoscale spin textures following femtosecond laser excitation. Specifically, we map quenched magnetic domains and localized spin structures in Co/Pd multilayers with a sub-wavelength spatial resolution down to 16 nm, and strobosocopically trace the local magnetization dynamics with 40 fs temporal resolution. Our approach enables the highest spatio-temporal resolution of magneto-optical imaging to date. Facilitating ultrafast imaging with an extreme sensitivity to various microscopic degrees of freedom expressed in chiral and linear dichroism, we envisage a wide range of applications spanning magnetism, phase transitions, and carrier dynamics.
Coherent anti-Stokes Raman scattering (CARS) and, in particular, femtosecond adaptive spectroscopic techniques (FAST CARS) have been successfully used for molecular spectroscopy and microscopic imaging. Recent progress in ultrafast nanooptics provides flexibility in generation and control of optical near fields, and holds promise to extend CARS techniques to the nanoscale. In this theoretical study, we demonstrate ultrafast subwavelentgh control of coherent Raman spectra of molecules in the vicinity of a plasmonic nanostructure excited by ultrashort laser pulses. The simulated nanostructure de…
The field of attosecond nanophysics, combining the research areas of attosecond physics with nanoscale physics, has experienced a considerable rise in recent years both experimentally and theoretically. Its foundation rests on the sub-cycle manipulation and sampling of the coupled electron and near-field dynamics on the nanoscale. Attosecond nanophysics not only addresses questions of strong fundamental interest in strong-field light-matter interactions at the nanoscale, but also could eventually lead to a considerable number of applications in ultrafast, petahertz-scale electronics, and ultra…
Spatiotemporal Terahertz Emission Nanoscopy of Spintronic Photocurrents
RPTU Kaiserslautern-Landau（凯泽斯劳滕-兰道莱布尼茨理工学院）；Fraunhofer Institute for Industrial Mathematics ITWM（弗劳恩霍夫工业数学研究所）；Freie Universität Berlin（柏林自由大学）；Hangzhou International Innovation Institute, Beihang University（北京航空航天大学杭州国际创新学院）；School of Electronic and Information Engineering, Beihang University（北京航空航天大学电子与信息工程学院）；School of Engineering, Brown University（布朗大学工程学院）；University of Lille, CNRS, Centrale Lille, Université Polytechnique Hauts-de-France（里尔大学、法国国家科学研究中心、中央里尔理工学院、上法兰西高等工业大学联合实验室）；Zhangjiang Laboratory（张江实验室）
Novel time-resolved imaging techniques for the investigation of ultrafast nanoscale magnetization dynamics are indispensable for further developments in light-controlled magnetism. Here, we introduce femtosecond Lorentz microscopy, achieving a spatial resolution below 100 nm and a temporal resolution of 700 fs, which gives access to the transiently excited state of the spin system on femtosecond timescales and its subsequent relaxation dynamics. We demonstrate the capabilities of this technique by spatio-temporally mapping the light-induced demagnetization of a single magnetic vortex structure…
We present a laboratory system for single-shot magneto-optical (MO) imaging of ultrafast magnetization dynamics with high-sensitivity of MO rotation. We create a stack of MO images repeatedly employing a single pair of a pump and defocused probe pulses to induce and visualize MO changes in the sample. Both laser beams are independently wavelength-tunable allowing for a flexible, resonant adjustable two-color pump and probe scheme. To increase the MO contrast the probe beam is spatially filtered. We performed the all-optical switching experiment in Co-doped yttrium iron garnet films (YIG:Co) to…
We report about the existence of magneto-acoustic pulses propagating in a 200-nm-thick ferromagnetic nickel film excited with 120 fs laser pulses. They result from the coupling between the magnetization of the ferromagnetic film and the longitudinal acoustic waves associated to the propagation of the lattice deformation induced by the femtosecond laser pulses. The magneto-acoustic pulses are detected from both the front and back sides of the film, using the time-resolved magneto-optical Kerr technique, measuring both the time dependent rotation and ellipticity. We show that the propagating aco…
Irradiation with an ultrashort laser pulse can completely destroy the magnetic order of ferromagnetic thin films on the femtosecond timescale. This phenomenon holds great potential for ultrafast spintronics and information processing and is an active field of research. It is still an open question if the angular momentum of light can support this effect. While it has been shown that the spin of light only has a negligible influence, we experimentally demonstrate the influence of ultrashort laser pulses with orbital angular momentum (OAM) on the magnetization dynamics of a thin nickel film. Our…
In this work, we report on modelling results obtained with our recently developed simulation tool enabling nanoscopic description of electronic processes in X-ray irradiated ferromagnetic materials. With this tool, we have studied the response of Co/Pt multilayer system irradiated by an ultrafast extreme ultraviolet pulse at the M-edge of Co (photon energy $\sim$ 60 eV). It was previously investigated experimentally at the FERMI free-electron-laser facility, using the magnetic small-angle X-ray scattering technique. Our simulations show that the magnetic scattering signal from cobalt decreases…
Ultrafast control of magnetization on the nanometer length scale, in particular all-optical switching, is key to putting ultrafast magnetism on the path towards future technological application in data storage technology. However, magnetization manipulation with light on this length scale is challenging due to the wavelength limitations of optical radiation. Here, we excite transient magnetic gratings in a GdFe alloy with a periodicity of 87 nm by interference of two coherent femtosecond light pulses in the extreme ultraviolet spectral range at the free electron laser facility FERMI. The subse…
Terahertz (THz) emission spectroscopy is a powerful method that allows one to measure the ultrafast dynamics of polarization, current, or magnetization in a material based on THz emission from the material. However, the practical implementation of this method can be challenging, and can result in significant errors in the reconstruction of the quantity of interest. Here, we experimentally and theoretically demonstrate a rigorous method of signal reconstruction in THz emission spectroscopy, and describe the main experimental and theoretical sources of reconstruction error. We identify the linea…
Ultrafast internal dynamics of chiral domain walls probed by time-resolved XRMS
Universität Siegen（锡根大学）；Elettra Sincrotrone Trieste（的里雅斯特 Elettra 同步辐射中心）；Ca' Foscari University of Venice（威尼斯卡福斯卡里大学）；Synchrotron SOLEIL（索莱尔同步辐射中心）；Johannes Gutenberg-Universität Mainz（美因茨约翰内斯·古腾堡大学）；Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay（阿尔贝·费尔特实验室，法国国家科学研究中心，泰雷兹集团，巴黎萨克雷大学）
Irradiating solids with ultrashort laser pulses is known to initiate femtosecond timescale magnetization dynamics. However, sub-femtosecond spin dynamics have not yet been observed or predicted. Here, we explore ultrafast light-driven spin dynamics in a highly non-resonant strong-field regime. Through state-of-the-art ab-initio calculations, we predict that a non-magnetic material can be transiently transformed into a magnetic one via dynamical extremely nonlinear spin-flipping processes, which occur on attosecond timescales and are mediated by a combination of multi-photon and spin-orbit inte…
Coherent diffractive imaging of individual free nanoparticles has opened novel routes for the in-situ analysis of their transient structural, optical, and electronic properties. So far, single-shot single-particle diffraction was assumed to be feasible only at extreme ultraviolet (XUV) and X-ray free-electron lasers, restricting this research field to large-scale facilities. Here we demonstrate single-shot imaging of isolated helium nanodroplets using XUV pulses from a femtosecond-laser driven high harmonic source. We obtain bright wide-angle scattering patterns, that allow us to uniquely iden…
Single-shot laser-pulse-induced magnetization reversal in CoFeB/MgO-based magnetic tunnel junctions
Université de Lorraine, CNRS, IJL（洛林大学）；National Institute of Advanced Industrial Science and Technology（产业技术综合研究所）；Tohoku University（东北大学）；Inamori Research Institute for Science（稻盛科学研究所）
