Abstract
Plasmonic dimer nanoantennas can significantly boost the electric field strength in the gap region, allowing for a modification of the feed gap geometry by femtosecond laser illumination. Using resonant bowtie antennas to enhance the electric field of a low-fluence femtosecond oscillator, here we experimentally demonstrate highly localized reshaping of the antennas, resulting in a self-optimization of the antenna shape. From high-resolution scanning electron micrographs and two-dimensional energy dispersive x-ray maps, we analyze the near-field enhanced subwavelength ablation at the nanotips and the resulting deposition of ablated materials in the feed gap. The dominant ablation mechanism is attributed to the nonthermal transient unbonding of atoms and electrostatic acceleration of ions. This process is driven by surface plasmon enhanced electron emission, with subsequent acceleration in the vacuum. This ablation is impeded in the presence of an ambient gas. A maximum of sixfold enhancement of the third-harmonic yield is observed during the reshaping process.
Highlights
Field enhancement by plasmonic nanoantennas promises access to strong-field nonlinear optics with high-repetition-rate nanojoule oscillator sources, including field-driven photoemission of electrons as well as generation of nonperturbative high harmonic generation (HHG) and incoherent deep-ultraviolet radiation [1,2,3,4,5,6]
We experimentally demonstrate a self-organized modification of gold bowtie nanoantennas during harmonic generation
It is shown that the modification of plasmonic nanoantennas through the irradiation of a femtosecond laser enables an additional boost of the harmonic conversion efficiency
Summary
Field enhancement by plasmonic nanoantennas promises access to strong-field nonlinear optics with high-repetition-rate nanojoule oscillator sources, including field-driven photoemission of electrons as well as generation of nonperturbative high harmonic generation (HHG) and incoherent deep-ultraviolet radiation [1,2,3,4,5,6]. The plasmon-assisted HHG from gas atoms is challenging [7], because first, the small volume of near-field enhancement limits the build-up of a coherent process, and second, the gold nanostructures do not withstand a strong laser field. We experimentally demonstrate a self-organized modification of gold bowtie nanoantennas during harmonic generation. It is shown that the modification of plasmonic nanoantennas through the irradiation of a femtosecond laser enables an additional boost of the harmonic conversion efficiency. The gaseous medium cannot support harmonic generation for our conditions, we found that it can be used to inhibit the ablation process
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