Subwavelenght Imaging of the Ultrafast Near-Field Dynamics of Single Gold Nanoantennas

Arthur Losquin Department of Physics, Lund University, Lund, Sweden Eleonora Lorek Department of Physics, Lund University, Lund, Sweden Erik Mårsell Department of Physics, Lund University, Lund, Sweden Miguel Miranda Department of Physics, Lund University, Lund, Sweden Chen Guo Department of Physics, Lund University, Lund, Sweden Anne Harth Department of Physics, Lund University, Lund, Sweden Robin Swärd Department of Physics, Lund University, Lund, Sweden Cord L. Arnold Department of Physics, Lund University, Lund, Sweden Anne L’Huillier Department of Physics, Lund University, Lund, Sweden Johan Mauritsson Department of Physics, Lund University, Lund, Sweden Anders Mikkelsen Department of Physics, Lund University, Lund, Sweden

Ultrafast applications of nanoplasmonics, such as near-field coherent control [1], are attracting a growing attention, stimulated by the progressive availability and mastering of ultrashort laser pulses. Such applications require reliable characterization tools to properly access the direct time evolution of near-fields induced by well-defined fs pulses, ultimately at the nanometer scale. Although recently successfully applied to micro and nanostructures, most of the optical techniques capable of characterizing ultrafast phenomena in time are limited by diffraction [2, 3]. On the other hand, PhotoEmission Electron Microscopy (PEEM) combined with fs lasers and optical interferometry setups is a highly relevant alternative tool to probe surface plasmon mediated near-field dynamics with nanometric spatial resolution, as suggested previously [4]. In this work, we combine PEEM with a broadband Ti:Sapphire oscillator delivering 6 fs pulses to investigate gold bowtie nanoantennas. Varying the size of the nanoantennas during the fabrication process allows tuning their field enhancement and dynamical response. We access the near-field dynamics at remarkably short times by recording fringe resolved subwavelength autocorrelation traces using an interferometric time-resolved setup. Combined with an accurate characterization of the incoming pulses, the results are compared to Finite Difference Time Domain numerical simulations.

Time-resolved PEEM measurements on gold bowtie nanoantennas.

a. SEM (left) and corresponding laser PEEM (right) images of small (1) and larger (2) nanoantennas. The laser beams are incident from the top, and the electric field vector lies in the sample plane. The spots occur within the gaps of the antennas. The white arrows indicate two very weak spots. The different intensities reflect different near-field enhancements. b. PEEM autocorrelation traces (positive short delays) corresponding to the small (blue) and larger antennas (red line). The traces show different ultrafast near-field dynamics (different widths and dephasing).

[1] M. I. Stockman et al., Phys. Rev. Lett. 88, 067402 (2002)

[2] A. Anderson et al., Nano Lett. 10, 2519 (2010)

[3] N. Accanto et al., Nano Lett. 14, 4078 (2014)

[4] A. Kubo et al., Nano Lett. 5, 1123 (2005)

arthur.losquin@fysik.lth.se