  We report about the experimental observation and characterization of
nonlinear optical properties of individual silicon nanowires of different
dimensions. Our results show that the nonlinear light has different components,
one of them corresponding to the second harmonic generation (SHG). The SHG
strongly depends on the polarization of the optical excitation and nanowire
diameter, and gives access to the local electromagnetic field intensity
distribution. Furthermore, we show that the second harmonic, when observed, is
enhanced compared to bulk silicon and is sensitive to optical resonances
supported by the nanowires. This offers different perspectives on the
definition of silicon-based nonlinear photonic devices.
