Sum-frequency generation spectroscopy is performed by spatially and temporally overlapping two femtosecond pulses. The addition of a femtosecond broadband white light spectrum (from ~450 to 1050 nm) to an 800 nm beam allows for the multiplexing of the nonlinear spectroscopy so that an entire spectrum may be acquired from each analysis. By using two beams, the chi squared properties are present which prevents the analysis of the bulk material. In the analysis of plasmon resonance of nanoparticles, the separation of the nonlinear signal from the surface is important in order to concentrate on the quadrupole plasmon resonance, instead of just the well-known dipole. The plasmon resonance of metal nanoparticles has been proven useful in areas such as thermal cancer therapy and cellular imaging, and the understanding of the effects of nanoparticle size, shape, and composition on the plasmon resonance is crucial to their use in these applications.