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Near-fields of non-resonantly laser-excited nanostructures enable strong localization of ultrashort light fields and have opened novel routes to fundamentally modify and control electronic strong-field processes. Harnessing spatiotemporally tunable near-fields for the steering of sub-cycle electron dynamics may enable ultrafast optoelectronic devices and unprecedented control in the generation of attosecond electron and photon pulses. Here we utilize unsupported sub-wavelength dielectric nanospheres to generate near-fields with adjustable structure and study the resulting strong-field dynamics via photoelectron imaging. We demonstrate field propagation-induced tunability of the emission direction of fast recollision electrons up to a regime, where nonlinear charge interaction effects become dominant in the acceleration process. Our analysis supports that the timing of the recollision process remains controllable with attosecond resolution by the carrier-envelope phase, indicating the possibility to expand near-field-mediated control far into the realm of high-field phenomena.

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A precise, real-time, single-shot carrier–envelope phase (CEP) tagging technique for few-cycle pulses was developed and combined with cold-target recoil-ion momentum spectroscopy and velocity-map imaging to investigate and control CEP-dependent processes with attosecond resolution. The stability and precision of these new techniques have allowed for the study of intense, few-cycle, laser-matter dynamics with unprecedented detail. Moreover, the same stereo above-threshold ionization (ATI) measurement was expanded to multi-cycle pulses and allows for CEP locking and pulse-length determination. Here we review these techniques and their first applications to waveform characterization and control, non-sequential double ionization of argon, ATI of xenon and electron emission from SiO2 nanospheres.

The promise of ultrafast light-field-driven electronic nanocircuits has stimulated the development of the new research field of attosecond nanophysics. An essential prerequisite for advancing this new area is the ability to characterize optical near fields from light interaction with nanostructures, with sub-cycle resolution. Here we experimentally demonstrate attosecond near-field retrieval for a tapered gold nanowire. By comparison of the results to those obtained from noble gas experiments and trajectory simulations, the spectral response of the nanotaper near field arising from laser excitation can be extracted.

Collective electron dynamics in plasmonic nanosystems can unfold on timescales in the attosecond regime and the direct measurements of plasmonic near-field oscillations is highly desirable. We report on numerical studies on the application of attosecond nanoplasmonic streaking spectroscopy to the measurement of collective electron dynamics in isolated Au nanospheres. The plasmonic field oscillations are induced by a few-cycle NIR driving field and are mapped by the energy of photoemitted electrons using a synchronized, time-delayed attosecond XUV pulse. By a detailed analysis of the amplitudes and phase shifts, we identify the different regimes of nanoplasmonic streaking and study the dependence on particle size, XUV photoelectron energy and emission position. The simulations indicate that the near-fields around the nanoparticles can be spatio-temporally reconstructed and may give detailed insight into the build-up and decay of collective electron motion.PACS numbers: 73.20.Mf, 78.47.JNanoplasmonics has rapidly evolved and numerous techniques have been developed to study the effects of plasmonic field enhancement 1 , but so far the direct, time-resolved measurement of plasmonic near-fields has not been achieved. The fastest dynamics in plasmonic nanosystems can take place on timescales down to 100 attoseconds as determined from the inverse bandwidth of plasmonic resonance spectra. Attosecond metrology has provided valuable tools for measurements of ultrafast electron dynamics in atoms 2-5 , molecules 6 and surfaces 7 . One of the most successful techniques is attosecond streaking spectroscopy 8,9 , employing photoemission of electrons by an attosecond XUV pulse synchronized to a strong optical field. Recording the electron kinetic energy spectra (by e.g. time-of-flight (TOF) spectroscopy) as a function of the delay between the two pulses allows for the reconstruction of the laser fields and the electron emission dynamics. The technique is consequently a promising candidate for the real-time observation of collective electron motion in nanosystems.One of the key aspects in traditional attosecond streaking on e.g. gas phase atomic targets is the spatial homogeneity of the driving laser field. In contrast, noble metal nanoparticles exhibit strongly enhanced, but highly localized optical fields, such that the assumption of spatial homogeneity is no longer valid. When applying attosecond streaking spectroscopy to nanoparticles, the spatial decay of the near-field into free space will govern the streaking process. Nanoplasmonic streaking was originally proposed for the instantaneous electric field probing regime 10 . A study on integrated streaking spectroscopy on nanostructured antennas showed, that a reconstruction of the relatively homogeneous field in the antenna gap is possible if photoemission is limited to this region 11 . Here the electron acceleration mostly takes place in the ponderomotive regime.We extend this previous work to spherical Au nanoparticles of different sizes and exploring the transition from t...

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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