Quantum-classical interface for optical interactions at Epsilon Near Zero

 Metallic optical properties derive from their dielectric function having Re<0 over a large frequency range that typically coincides with the visible optical spectrum, where metals are strongly reflective. At =0 metals transmit electromagnetic fields as charge density waves, or bulk plasmons. Thus, it is interesting to investigate the single-particle and collective optical responses of metals through the Epsilon Near Zero (ENZ) region. We apply the coherent time-resolved photoemission electron spectroscopy and microscopy to investigate the optical responses of Ag from the perspective of both the single particle and collective excitations in a regime at the interface of classical-quantum physics through the ENZ region. I will describe how the collective plasmonic responses decay into single particles, how the optical field affects single particle excitations, and generation of a new quasiparticle by excitation of plasmonic modes with structured light.