Plasmonic nanoantennas emit two-photon photoluminescence, which is much stronger than their second harmonic generation. Unfortunately, luminescence is an incoherent process and therefore generally not explored for nanoscale coherent control of the antenna response. Here, we demonstrate that, in resonant gold nanoantennas, the two-photon absorption process can be coherent, provided that the excitation pulse duration is shorter than the dephasing time of plasmon mode oscillation. Exploiting this coherent response, we show the pure spectral phase control of resonant gold nanoantennas, with effective read-out of the two-photon photoluminescence.

Using single molecule localization microscopy, we let molecules stochastically probe the near field of nanorods. By statistical analysis we identify weaker versus stronger interaction and create 2D interaction maps for different resonance conditions.

Plasmonic nanostructures dramatically alter the radiative and non-radiative properties of single molecules in their vicinity. This coupling induced change in decay channels selectively enhances specific vibronic transitions, which can enable plasmonic control of molecular reactivity. Here, we report coupling dependent spectral emission shaping of single Rhodamine 800 molecules in the vicinity of plasmonic gold nanorods. We show that the relative vibronic transition rates of the first two vibronic transitions of the spontaneous emission spectrum can be tuned in the weak coupling regime, by approximately 25-fold, on the single molecule level.

Nanoscale phase-control is one of the most powerful approaches to specifically tailor electrical fields in modern nanophotonics. Especially the precise sub-wavelength assembly of many individual nano-building-blocks has given rise to exciting new materials as diverse as metamaterials, for miniaturizing optics, or 3D assembled plasmonic structures for biosensing applications. Despite its fundamental importance, the phase-response of individual nanostructures is experimentally extremely challenging to visualize. Here, we address this shortcoming and measure the quantitative scattering phase of different nanomaterials such as gold nanorods and spheres as well as dielectric nanoparticles. Beyond reporting spectrally resolved responses, with phase-changes close to π when passing the particles' plasmon resonance, we devise a simple method for distinguishing different plasmonic and dielectric particles purely based on their phase behavior. Finally, we integrate this novel approach in a single-shot two-color scheme, capable of directly identifying different types of nanoparticles on one sample, from a single widefield image.Phase, an elusive quantity in day-to-day life, is one of the most crucial parameters in physics and the lifesciences. Historically, measurements based on phase-contrast have proven to be extremely powerful and highly sensitive to tiny changes in the morphology of structures 1 even if the underlying absolute phasevalue remained unobserved. Since these pioneering works, technology has advanced rapidly and different phase-detecting techniques are of crucial importance across many scientific fields. In nanoscale physics, the phase of a nanoparticle (NP) accesses its nanoscale response 2-5 and is a crucial parameter for tailoring complex photonic structures such as metasurfaces which manipulate the amplitude, direction and polarization of light at nano-to micro-scales 6,7 . In the biomedical sciences, phase-based measurements are often key enablers for ultrasensitive measurements 8 such as protein-binding to plasmonic structures [9][10][11] and the emerging field of quantitative phase imaging is expected to dramatically contribute to future diagnostics 12,13 . However, even though macro-scale phase measurements are relatively easy to implement, determining the absolute scattering phase of individual nano-objects is far from trivial as one has to consider the phase of the observation wave and account for the sub-diffraction limited nature of the particle. A versatile experimental approach to directly and reproducibly determine the absolute phase of such objects would both advance the observation-based development of nanophotonic materials and allow implementing novel imaging methodologies that exploit absolute phase measurements as a robust contrast mechanism for distinguishing and identifying different materials in a complex environment.