Time-Resolved Spectroscopy of Laser-Induced Light Emission from an Evaporated Au Film in the Kretschmann Geometry

We have investigated laser-induced light emission from Au film evaporated on the bottom of a hemispherical glass prism in the Kretschmann geometry. Picosecond laser pulses tuned at a photon energy of 1.35 eV were focused onto the Au film from the vacuum side of the prism, and the time- and photon-energy-resolved spectra of light emitted through the prism were measured in a photon energy range from 1.5 to 2.5 eV for a time span of 2 ns by a streak camera operated in synchronization with the laser pulses. The total intensity of emission was proportional to the square of incident laser power, suggesting that the emission is excited via a second order nonlinear optical process. The time-integrated spectrum of the emission was successfully reproduced by the dielectric theory of light emission that treats radiation by surface plasmon polaritons (SPP) confined in this sample structure. Hence we see that the emission is radiated by SPP being excited via the nonlinear optical process. This feature is not consistent with the temporal behavior of emission, i.e., the lifetime of the emission was as long as 240 ps.