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Center for Nonlinear Studies |
The chemical composition of atmospheric aerosols is a crucial factor in their contribution to air pollution and their impact on health. Strong laser fields offer a route for single particle chemical analysis, where molecular fragments are created in the laser interaction and spectroscopically identified. Strong-field induced processes in molecules such as ionization and dissociation have been subject to theoretical and experimental investigations for many decades. These processes include, e.g., above threshold ionization, high harmonic generation, and laser induced electron diffraction. Since these effects strongly rely on the exact spatial and temporal evolution of the electric fields, they are also influenced and controlled by the presence of enhanced near-fields in the proximity of a nanostructure [1,2]. We have theoretically and experimentally studied near-field driven photoemission from nanostructures on attosecond to femtosecond timescales (e.g. [3-6]). We find that field localization at nanostructures illuminated with laser pulses of well-defined waveform enables spatial-temporal tailoring of the near-fields permitting sub-cycle control of electron dynamics at the nanoscale [3,4]. The corresponding near-fields can be sampled on attosecond timescales [5] and recent work on dielectrics provides insight into attosecond electron scattering dynamics inside the particles [6], see figure. We have extended our research on electron dynamics in nanoparticles and developed a nanotarget reaction-microscope based on recoil-ion-momentum spectroscopy (nanoTRIMS) [7]. The novel device permits recording both ions and electrons from the interaction of light pulses with molecules on a nanoparticle surface. In a first implementation of nanoTRIMS, we studied proton formation from water and ethanol molecules on SiO2 surfaces and found that the reactions are driven by the local near-fields. The nanoTRIMS enables us to obtain spatially resolved reaction rates on the particle surface. The results open the door towards strong near-field induced chemical reactions on nanoparticles and a route towards nanometer-scale spatio-selective chemical analysis of molecular adsorbates on aerosols.
[1] P. Hommelhoff and M.F. Kling, Attosecond Nanophysics: From Basic Science to Applications, (Wiley, 2015)[2] M.F. Ciappina et al., Attosecond physics at the nanoscale, Rep. Progr. Phys. 80, 054401 (2017).[3] S. Zherebtsov et al., Controlled near-field enhanced electron acceleration from dielectric nanospheres with intense few-cycle laser fields, Nature Phys. 7, 656 (2011).[4] F. Süßmann et al., Field propagation induced directionality of carrier-envelope phase controlled photoemission from nanospheres, Nature Comm. 6:7944 (2015).[5] B. Förg et al., Attosecond nanoscale near-field sampling, Nature Comm. 7, 11717 (2016).[6] L. Seiffert et al., Attosecond chronoscopy of electron scattering in dielectric nanoparticles, Nature Phys. 13, 766 (2017).[7] P. Rupp et al., submitted.
Host: Alexis Chacon