The most general investigation and exploitation of light-induced processes require simultaneous control over spatial and temporal properties of the electromagnetic field on a femtosecond time and nanometer length scale. Based on the combination of polarization pulse shaping and time-resolved two-photon photoemission electron microscopy, we demonstrate such control over nanoscale spatial and ultrafast temporal degrees of freedom of an electromagnetic excitation in the vicinity of a nanostructure. The time-resolved cross-correlation measurement of the local photoemission yield reveals the switching of the nanolocalized optical near-field distribution with a lateral resolution well below the diffraction limit and a temporal resolution on the femtosecond time scale. In addition, successful adaptive spatiotemporal control demonstrates the flexibility of the method. This flexible simultaneous control of temporal and spatial properties of nanophotonic excitations opens new possibilities to tailor and optimize the lightmatter interaction in spectroscopic methods as well as in nanophotonic applications.coherent control | nanophotonics | plasmonics | ultrafast spectroscopy T he interaction of light with matter is of fundamental importance in many areas of nature, science, and engineering, and the dynamics and efficiency of light-induced processes are determined by the properties of the optical field as a function of space and time at the location of interaction. Hence their most general investigation and exploitation would require the generation of light fields that can be specified at will in both their spatial and temporal degrees of freedom at all length and time scales. In the past, significant progress has been made toward realizing either of these two manipulation objectives separately. For temporal field properties, femtosecond laser pulse shaping (1) offers flexible control over the field amplitude, phase, and polarization (2, 3) on an ultrashort time scale. This has been exploited for coherent control over numerous quantum-mechanical systems (4, 5). For the case of spatial light-field properties, on the other hand, emerging nanooptical techniques (6) have made available spectroscopy beyond the Abbe diffraction limit, as, for example, nanoantenna-assisted addressing of individual molecules (7). Combination with femtosecond excitation offers high resolution in space and time (8-15) and opens routes toward novel applications (16,17). In particular, deliberate spatial manipulation of optical near-field distributions was realized with adaptive and coherent control methods (9,(11)(12)(13)(18)(19)(20)(21)(22). In our recent demonstration of adaptive control of nanooptical fields (13), only spatial properties of optical near-field distributions were accessed. In the present work, in contrast, we directly measure and control also the temporal evolution of the nanoscale excitation. This information is obtained and exploited here using time-resolved cross-correlation measurements with one polarization-shaped "pump" light pu...

No abstract

No abstract

Optimal open-loop control, i.e. the application of an analytically derived control rule, is demonstrated for nanooptical excitations using polarization-shaped laser pulses. Optimal spatial near-field localization in gold nanoprisms and excitation switching is realized by applying a π shift to the relative phase of the two polarization components. The achieved near-field switching confirms theoretical predictions, proves the applicability of predefined control rules in nanooptical light-matter interaction and reveals local mode interference to be an important control mechanism.

The authors introduce a method for cross correlating vacuum-ultraviolet with near-infrared femtosecond light pulses in a perpendicular geometry. Photoelectrons generated in an atomic gas by laser-assisted photoionization are used to create a two-dimensional image of the cross-correlation volume, thereby mapping time onto a space coordinate. Thus, information about pulse duration and relative timing between the pulses can be obtained without the need to scan an optical delay line. First tests using vacuum-ultraviolet pulses from the free-electron laser at the Deutsches Elektronen Synchrotron set an upper limit for their temporal jitter with respect to external optical laser pulses. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2714999͔For measurement of the temporal properties of optical pulses in the visible, near-ultraviolet, and near-infrared ͑NIR͒ range the nonlinear response of an optical medium-usually a crystal-on two optical fields of different or the same color is often used to realize cross-or autocorrelation schemes. 1 The recent advent of sources of femtosecond-and even attosecond 2 -pulses of ionizing radiation, based on laser plasmas, 3 high harmonic generation, 4 and free-electron lasing calls for a transfer of the correlation principle to the vacuum-ultraviolet ͑vuv͒ and the x-ray range. Since, however, crystals are no longer transparent in the vuv and do not exhibit sufficient nonlinearity in the x-ray range, alternative approaches for pulse characterization are necessary. Freeelectron lasers ͑FELs͒ are the most powerful femtosecond laser sources at short wavelengths, currently operating in the vuv range ͓e.g., free-electron laser Hamburg ͑FLASH͔͒ 5 and down to x-rays in the future. 6,7 So far, the utilized mode of operation for short-wavelength FELs relies on the process of self-amplified spontaneous emission ͑SASE͒. 8 High photon energies combined with greatly enhanced pulse intensities as compared to other sources make FELs a promising source for time-resolved visible/vuv pump-probe studies. FELs, however, are based on linear accelerators and undulators, which together measure from a few hundred meters up to a few kilometers in length. This makes these instruments susceptible to path length variations on a micrometer scale. Moreover, the statistical nature of SASE comes with a frequently varying spectral and temporal profile for each individual shot. 9 As a result, the arrival time of the FEL pulses at the experiment fluctuates in the order of a few hundred femtoseconds. This jitter inhibits an exact synchronization to an external laser source needed for reliable pump-probe studies. Therefore, an adequate characterization method is needed to determine the pulse duration together with the actual delay with respect to an external laser on a shot-to-shot basis. State-of-the-art x-ray streak cameras have reached subpicosecond temporal resolution, 10 but the photocathode completely dissipates the beam. In addition, their readout rate is limited to a few hertz, while FLASH is operated at a...