Resonant-Plasmon-Assisted Subwavelength Ablation by a Femtosecond Oscillator

International audienceWe experimentally demonstrate the use of subwavelength optical nanoantennas to assist a direct nanoscale ablation using the ultralow fluence of a Ti:sapphire oscillator through the excitation of surface plasmon waves. The mechanism is attributed to nonthermal transient unbonding and electrostatic ablation, which is triggered by the surface plasmon-enhanced field electron emission and acceleration in vacuum. We show that the electron-driven ablation appears for both nanoscale metallic as well as dielectric materials. While the observed surface plasmon-enhanced local ablation may limit the applications of nanostructured surfaces in extreme nonlinear nanophotonics, it, nevertheless, also provides a method for nanomachining, manipulation, and modification of nanoscale materials. Collateral thermal damage to the antenna structure can be suitably avoided, and nonlinear conversion processes can be stabilized by a dielectric overcoating of the antenna

Self-optimization of plasmonic nanoantennas in strong femtosecond fields

International audiencePlasmonic 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

A femtosecond X-ray/optical cross-correlator

For a fundamental understanding of ultra fast dynamics in chemistry, biology and materials science it has been a longstanding dream to record a molecular movie, where both the atomic trajectories and the chemical state of every atom in matter is followed in real time. Free-electron lasers (FEL) provide this perspective as they deliver brilliant femtosecond X-ray pulses spanning a wide photon energy range, which is necessary to gather element-specific and chemical-state-selective information with femtosecond time resolution. The key challenge lies in synchronizing the FEL with separate optical lasers. We exploit the peak brilliance of the FEL in Hamburg (FLASH) and establish X-ray pulse induced transient changes of the optical reflectivity in GaAs as a powerful tool for X-ray/optical cross-correlation. This constitutes a breakthrough en route to a molecular movie and – equally important – opens the novel field of femtosecond X-ray induced dynamics, only accessible with high brilliance X-ray free-electron lasers

Search for Multi-messenger Sources of Gravitational Waves and High-energy Neutrinos with Advanced LIGO during its first Observing Run, ANTARES and IceCube

Astrophysical sources of gravitational waves, such as binary neutron star and black hole mergers or core-collapse supernovae, can drive relativistic outflows, giving rise to non-thermal high-energy emission. High-energy neutrinos are signatures of such outflows. The detection of gravitational waves and high-energy neutrinos from common sources could help establish the connection between the dynamics of the progenitor and the properties of the outflow. We searched for associated emission of gravitational waves and high-energy neutrinos from astrophysical transients with minimal assumptions using data from Advanced LIGO from its first observing run O1, and data from the ANTARES and IceCube neutrino observatories from the same time period. We focused on candidate events whose astrophysical origin could not be determined from a single messenger. We found no significant coincident candidate, which we used to constrain the rate density of astrophysical sources dependent on their gravitational wave and neutrino emission processes