Noncollinear excitation of surface electromagnetic waves: Enhancement of nonlinear optical surface response

We excite several independent surface electromagnetic waves on a metallic surface by use of femtosecond laser pulses of different frequencies. Due to nonlinear plasmon interaction, optical radiations at frequencies $2\omega ,$ ${\omega }_1+{\omega }_2,$ and $2{\omega }_2-{\omega }_1$ are generated (where ${\omega }_1$ and ${\omega }_2$ correspond laser beam frequencies). In the present paper we report experimental results and theoretical modeling of these multiphoton nonlinear optical effects from a metallic film sputtered onto a grating surface. The theoretical approach we use describes the multiphoton nonlinear optical effects in the presence of noncollinear interacting surface electromagnetic waves. In the experiments a sufficient enhancement of the nonlinear optical signals is achieved in the case where the incidence plane of light is parallel to the grating grooves.