초록/요약

A plasmonic chiral metamaterial is fabricated from a thin Au film and exhibits static optical rotatory power (ORP) in the visible spectral range. Transient ORP is measured to clarify the temporal development of ORP using a circularly polarized light (CPL) pump beam. Three distinct transient behaviors of ORP are identified, resulting from different energy relaxation processes of hot electrons that occur during a period of a few picoseconds after pumping. Nonthermal hot electrons experience Lorentz force from an inverse Faraday effect and electron-boundary scattering, yielding a pump beam CPL helicity-dependent transient ORP. Once hot electrons are in thermal equilibrium with the lattice, electron energy is distributed among the occupied states, as described by Fermi-Dirac statistics. Moreover, the transient ORP is independent of pump beam CPL helicity, well explained by the selection rule of electron excitation and two-temperature model of the electron cooling process. Theoretical analysis of the transient ORP in terms of the energy relaxation of thermal hot electrons is carried out by introducing a temperature-dependent dielectric function and finite-difference time-domain simulation. It is found that the magnitude of ORP at an elevated temperature is reduced to less than that at room temperature, agreeing well with the experimental observation.