Femtosecond laser near-field ablation from gold nanoparticles

Short-pulse laser ablation is promising owing to the low threshold for material removal from surfaces. In the laser-ablation process, solid material transforms into a volatile phase initiated by a rapid deposition of energy. Explosive boiling can be one of the mechanisms in which matter is heated close to the critical point. Other pathways of non-thermal excitation will be present for very short laser pulses(1). Here we observe a different channel of ablation from gold nanoparticles, which takes place below the particle melting point. This process is induced by the optical near-field, a subwavelength field enhancement close to curved surfaces, in particular. Using picosecond X-ray scattering, we can track the temporal and energetic structural dynamics during material ejection from the nanoparticles. This effect will limit any high-power laser manipulation of nanostructured surfaces, such as surface-enhanced Raman measurements(2) or plasmonics with femtosecond pulses.