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.

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.

Strong laser fields can be used to trigger an ultrafast molecular response that involves electronic excitation and ionization dynamics. Here, we report on the experimental control of the spatial localization of the electronic excitation in the C 60 fullerene exerted by an intense few-cycle (4 fs) pulse at 720 nm. The control is achieved by tailoring the carrier-envelope phase and the polarization of the laser pulse. We find that the maxima and minima of the photoemission-asymmetry parameter along the laser-polarization axis are synchronized with the localization of the coherent electronic wave packet at around the time of ionization. DOI: 10.1103/PhysRevLett.114.123004 PACS numbers: 33.80.Eh, 31.15.xv, 42.50.Hz, 71.20.Tx Electrons determine the forces on the nuclei in molecules. Tuning the nonequilibrium electronic dynamics before the onset of significant nuclear motion opens new routes for tailoring chemical reactivity. For few-cycle optical pulses, varying the phase between the envelope and the field amplitude [carrier-envelope phase (CEP)] can be used to control electronic dynamics induced in molecules during the interaction with the pulse [1][2][3]. Electronic dynamics are typically probed indirectly by recording molecular fragmentation patterns of dissociative (ionization) channels exploiting the coupling between the electronic and nuclear degrees of freedom . The analysis of the fragmentation patterns is usually complex-even for simple diatomic molecules-and quickly becomes prohibitively complicated for large polyatomic molecules because of the large number of fragmentation channels [3]. Angularly resolved photoionization by ultrashort laser pulses has been advocated for probing the electronic dynamics before the onset of significant nuclear motion (see, e.g., [27][28][29][30][31] [36,37], and efficient high-harmonic generation [38][39][40]. The ionization and fragmentation of C 60 have been investigated extensively in the past (see, e.g., [35,[41][42][43][44][45][46][47]). C 60 is very stable and is one of the few molecular systems for which the ionization energy is smaller than the lowest fragmentation threshold. Therefore it is an ideal system for probing electronic dynamics, and, when suitably excited, the electronic density oscillates on a nanometer scale. Moreover, in the experiments reported here, the pulse duration is short enough to avoid significant thermionic emission that occurs for longer pulse durations of hundreds of femtoseconds to nanoseconds [48,49]. In this Letter, we demonstrate the control over transient electronic dynamics in a large polyatomic system, the C 60 fullerene, and we find that the angular distribution of direct photoelectrons reflects the spatial localization of the electronic wave packet at about the time of ionization.The electron emission from C 60 as a function of the CEP is recorded with phase-tagged velocity-map imaging (VMI) [50]. Details of the experimental setup are contained in the Supplemental Material [51]. The few-cycle laser pulses are focused into the VM...