Two thirds of the surface of our planet are covered by water and are still poorly instrumented, which has prevented the earth science community from addressing numerous key scientific questions. The potential to leverage the existing fiber optic seafloor telecom cables that criss-cross the oceans, by using them as dense arrays of seismo-acoustic sensors, remains to be evaluated. Here, we report Distributed Acoustic Sensing measurements on a 41.5 km-long telecom cable that is deployed offshore Toulon, France. Our observations demonstrate the capability to monitor with unprecedented details the ocean-solid earth interactions from the coast to the abyssal plain, in addition to regional seismicity (e.g., a magnitude 1.9 micro-earthquake located 100 km away) with signal characteristics comparable to those of a coastal seismic station.
Optical nanoantennas confine light on the nanoscale, enabling strong light-matter interactions and ultracompact optical devices. Such confined nanovolumes of light have nonzero field components in all directions (x, y, and z). Unfortunately mapping of the actual nanoscale field vectors has so far remained elusive, though antenna hotspots have been explored by several techniques. In this paper, we present a novel method to probe all three components of the local antenna field. To this end a resonant nanoantenna is fabricated at the vertex of a scanning tip. Next, the nanoantenna is deterministically scanned in close proximity to single fluorescent molecules, whose fixed excitation dipole moment reads out the local field vector. With nanometer molecular resolution, we distinctly map x-, y-, and z-field components of the dipole antenna, i.e. a full vectorial mode map, and show good agreement with full 3D FDTD simulations. Moreover, the fluorescence polarization maps the localized coupling, with emission through the longitudinal antenna mode. Finally, the resonant antenna probe is used for single molecule imaging with 40 nm fwhm response function. The total fluorescence enhancement is 7.6 times, while out-of-plane molecules, almost undetectable in far-field, are made visible by the strong antenna z-field with a fluorescence enhancement up to 100 times. Interestingly, the apparent position of molecules shifts up to 20 nm depending on their orientation. The capability to resolve orientational information on the single molecule level makes the scanning resonant antenna an ideal tool for extreme resolution bioimaging.
Cavity quantum electrodynamics is the art of enhancing light-matter interaction of photon emitters in cavities with opportunities for sensing, quantum information, and energy capture technologies. To boost emitter-cavity interaction, that is, coupling strength g, ultrahigh quality cavities have been concocted yielding photon trapping times of microsecondsy to milliseconds. However, such high- Q cavities give poor photon output, hindering applications. To preserve high photon output, it is advantageous to strive for highly localized electric fields in radiatively lossy cavities. Nanophotonic antennas are ideal candidates combining low- Q factors with deeply localized mode volumes, allowing large g, provided the emitter is positioned exactly right inside the nanoscale mode volume. Here, with nanometer resolution, we map and tune the coupling strength between a dipole nanoantenna-cavity and a single molecule, obtaining a coupling rate of g ∼ 200 GHz. Together with accelerated single photon output, this provides ideal conditions for fast and pure nonclassical single photon emission with brightness exceeding 10 photons/sec. Clearly, nanoantennas acting as "bad" cavities offer an optimal regime for strong coupling g to deliver bright on-demand and ultrafast single photon nanosources for quantum technologies.
Picosecond thermoreflectance is an unprecedented powerful technique for nanoscale heat transfer analysis and metrology, but different sources of artifacts were reported in the literature making this technique difficult to use for long delay (several ns) thermal analysis. We present in this paper a new heterodyne picosecond thermoreflectance (HPTR) technique. As it uses two slightly frequency shifted lasers instead of a mechanical translation stage, it is possible to avoid all artifacts leading to erroneous thermal parameter identifications. The principle and set-up are described as well as the model. The signal delivered by the HPTR experiment is calculated for each excitation configurations, modulating or not the pump beam. We demonstrate the accuracy of the technique in the identification of the thermal conductivity of a 50 nm thick SiO2 layer. Then, we discuss the role of the modulation frequency for nanoscale heat transfer analysis.
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