For a critical film thickness we find a large resonant enhancement of second-harmonic generation by surface polaritons. The effect is due to perfect phase matching between surface polaritons on different branches of the surface-polariton dispersion curve. For the case of a free-standing copper film in the infrared, our calculation predicts a surface second-harmonic intensity 3000 times larger than that found at the surface of the semi-infinite metal.

• Received 12 November 1985

DOI:https://doi.org/10.1103/PhysRevB.33.6775