2018-01-05, Liu, Q., Seiffert, L., Trabattoni, A., Castrovilli, M.C., Galli, M., Rupp, P., Frassetto, F., Poletto, L., Nisoli, M., Rühl, E., Krausz, F., Fennel, T., Zherebtsov, S., Calegari, F., Kling, M.F.

The development of attosecond metrology has enabled time-resolved studies on atoms, molecules, and (nanostructured) solids. Despite a wealth of theoretical work, attosecond experiments on isolated nanotargets, such as nanoparticles, clusters, and droplets have been lacking. Only recently, attosecond streaking metrology could be extended to isolated silica nanospheres, enabling real-time measurements of the inelastic scattering time in dielectric materials. Here, we revisit these experiments and describe the single-shot analysis of velocity-map images, which permits to evaluate the recorded number of electrons. Modeling of the recorded electron histograms allows deriving the irradiated nanoparticle statistics. Theoretically, we analyze the influence of the nanoparticle size on the field-induced delay, which is one of the terms contributing to the measured streaking delay. The obtained new insight into attosecond streaking experiments on nanoparticles is expected to guide wider implementation of the approach on other types of nanoparticles, clusters, and droplets.

2012, Zherebtsov, S., Süßmann, F., Peltz, C., Plenge, J., Betsch, K.J., Znakovskaya, I., Alnaser, A.S., Johnson, N.G., Kübel, M., Horn, A., Mondes, V., Graf, C., Trushin, S.A., Azzeer, A., Vrakking, M.J.J., Paulus, G.G., Krausz, F., Rühl, E., Fennel, T., Kling, M.F.

Waveform-controlled light fields offer the possibility of manipulating ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is key to the design of electronic devices operating at up to petahertz frequencies. We have studied the directional control of the electron emission from 95 nm diameter SiO 2 nanoparticles in few-cycle laser fields with a well-defined waveform. Projections of the three-dimensional (3D) electron momentum distributions were obtained via single-shot velocity-map imaging (VMI), where phase tagging allowed retrieving the laser waveform for each laser shot. The application of this technique allowed us to efficiently suppress background contributions in the data and to obtain very accurate information on the amplitude and phase of the waveform-dependent electron emission. The experimental data that are obtained for 4 fs pulses centered at 720 nm at different intensities in the range (1-4)×10 13Wcm -2 are compared to quasi-classical mean-field Monte-Carlo simulations. The model calculations identify electron backscattering from the nanoparticle surface in highly dynamical localized fields as the main process responsible for the energetic electron emission from the nanoparticles. The local field sensitivity of the electron emission observed in our studies can serve as a foundation for future research on propagation effects for larger particles and field-induced material changes at higher intensities.

2014, Heissler, P., Lugovoy, E., Hörlein, R., Waldecker, L., Wenz, J., Heigoldt, M., Khrennikov, K., Karsch, S., Krausz, F., Abel, B., Tsakiris, G.D.

High harmonic generation on solid and gaseous targets has been proven to be a powerful platform for the generation of attosecond pulses. Here we demonstrate a novel technique for the XUV generation on a smooth liquid surface target in vacuum, which circumvents the problem of low repetition rate and limited shot numbers associated with solid targets, while it maintains some of its merits. We employed atomically smooth, continuous liquid jets of water, aqueous salt solutions and ethanol that allow uninterrupted high harmonic generation due to the coherent wake emission mechanism for over 8 h. It has been found that the mechanism of plasma generation is very similar to that for smooth solid target surfaces. The vapor pressure around the liquid target in our setup has been found to be very low such that the presence of the gas phase around the liquid jet could be neglected.