The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and ...understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism.
The possibility of material surfaces restructuring on the nanoscale due to ultrashort laser pulses has recently found a number of practical applications. It was found experimentally that under ...spatial confinement due to a liquid layer atop the surface, one can achieve even finer and cleaner structures as compared to that in air or in vacuum. The mechanism of the materials restructuring under the liquid confinement, however, is not clear and its experimental study is limited by the extreme conditions realized during the intense and localized laser energy deposition that takes place on nanometer spatial and picosecond time-scales. In this theoretical work, we suggest a molecular dynamics-based approach that is capable of simulating the processes of periodic nanostructuring with ultrashort UV laser pulse on metals. The theoretical results of the simulations are directly compared with the experimental data on the same spatial and temporal scales.
•It is well known that the electron–phonon coupling plays a fundamental role in ultrafast laser-matter processing.•A few years ago, this parameter has been calculated for several materials in a large ...range of temperatures.•Here we show for the example of gold that the electronic temperature is not a proper variable, but rather the complete distribution of free electrons influences the coupling strongly.
Exciting a metal by an ultrashort laser pulse, the electrons are driven out of thermal equilibrium, while the phonon system remains almost unaffected. During and after the irradiation, the electrons thermalize and transfer energy to the phonons. In this work, we investigate the electron–phonon coupling in gold. The dependence of the coupling strength on the phonon properties as well as the nonequilibrium electrons has been taken into account. For the phonon system, we utilize several phonon temperatures. For the electrons we apply different excitation scenarios depending on the laser fluence and the photon energy. We observe that for gold at electron temperatures below 2000K, the phonon distribution may affect the coupling slightly. However, the electron distribution, especially under nonequilibrium conditions, governs the electron–phonon coupling factor significantly.
Nanoprocessing of materials using ultrashort laser pulses involves a number of concurrent fundamental physical processes. Due to different time and spatial scales of activation, however, these ...processes are difficult to study within the frames of a single computational model on one hand, and yet not possible to isolate in the experimental analysis on the other hand. In their detailed investigation, the transient character of the nonequilibrium states of matter induced with a short laser pulse hampers the applicability of continuum approaches, but classical molecular dynamics simulations are usually limited in the system sizes. In this work, a molecular dynamics based model coupled to a continuum description of the photo-excited free carrier’s dynamics and implemented in parallel algorithm is extended to the scale directly accessible in the experiment. This allows for the first time a direct comparison to experimental data. The essential mechanisms responsible for the short laser pulse surface nanostructuring are analyzed in the complex dynamics of competing processes simultaneously involved into the nanostructures generation process. The modeling and experiment show a very good agreement and predict a new opportunity for fabrication of nanoparticle structures and the surface subpatterning.
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