Phys. Rev. Lett. 108, 136802 (2012)

Nicolai Grosse, Jan Heckmann and Ulrike Woggon from the Technische Universität Berlin have investigated the roles played by various optical modes during enhanced second-harmonic generation inside a metal-nanofilm-covered prism. Employing the Kretschman geometry caused the modes in the prism to be excited when the tangential component of the incident beam's wavevector was equal to the wave number of the modes guided along the metal film. The researchers used k-space spectroscopy to separate different modes according to their wavenumber and varied the angle of incidence to determine the contribution of each mode to the second-harmonic generation signal. As expected, the main second-harmonic generation peak coincided with the resonant excitation of a plasmonic mode and hence a higher local electric field to drive the process. The researchers hope that this particular spectroscopic set-up will be useful for investigating nonlinear interactions in more complex nanometallic structures.