Optical second-harmonic generation with surface plasmons in noncentrosymmetric crystals

Abstract

We report an extensive investigation of optical second-harmonic generation (SHG) with the simultaneous excitation of the surface-plasmon (SP) mode at the interface between a metal and a nonlinear piezoelectric crystal. The birefringence of appropriately oriented potassium dihydrogen phosphate (KDP) crystals is utilized to demonstrate both quasi-phase-matched reflected SHG and transmitted SHG with fundamental SP excitation. The effect on the SHG resonances of the softness of the KDP crystal is discussed. Resonant SHG with fundamental SP excitation is observed for Al- and Ag-metal films on variously oriented quartz crystals. The source of the SHG for the $X$-cut orientation is the nonlinear crystal while for the $Z$-cut orientation it is the metal film. This latter result indicates that the recent observations of DeMartini et al. [Phys. Rev. B 23, 3797 (1980)] must be reinterpreted. In all our experiments, even including those in which a crystal with a large nonlinear susceptibility such as ${\mathrm{LiIO}}_{3}$ is utilized, the predicted SHG resonance due to the nonlinearly excited harmonic SP mode is always masked by the nonresonant SHG contribution from the metal itself.