Ultrafast Meets Ultrasmall: Controlling Nanoantennas and Molecules

We present a review on the advances of pulse control and ultrafast coherent excitation of both plasmonic nanoantennas and individual molecular systems, primarily based on the achievements in our group. Essential concepts from coherent control of ultrashort broadband laser pulses are combined with nanoscale diffraction limited detection and imaging of single photon emitters; that is, the central area of this work is where ultrafast meets ultrasmall. First, the critical role of dedicated pulse shaping and phase control is discussed, which is crucial to realize free of spatiotemporal coupling Fourier limited pulses inside a high numerical aperture microscope at the diffraction limited spot. Next we apply this scheme to plasmonic antennas, exploiting broadband two-photon excitation, to determine amplitude and phase of plasmonic resonances, to achieve ultrafast switching of nanoscale hotspots, and multicolor second harmonic detection for imaging applications. Subsequently, we address single molecules with phase-shaped pulses to control the electronic state population and retrieve single molecule vibrational dynamics response. We compare the response of a molecule to phase-locked with free phase multipulse excitation. Furthermore, we discuss phase control of excited state energy transfer in photosynthetic molecular complexes. Finally, we combine nanoscale plasmonics with single molecule detection to attain strong enhancement of both excitation and emission, with fluorescence lifetime shortening to the ps range. In conclusion, we anticipate that this review on ultrafast plasmonics and single emitter control will provide a useful view of the status of ultrafast nanophotonics and its application potential.