Sensing with multipolar second harmonic generation from spherical metallic nanoparticles.

We show that sensing in the nonlinear optical regime using multipolar surface plasmon resonances is more sensitive in comparison to sensing in the linear optical regime. Mie theory, and its extension to the second harmonic generation from a metallic nanosphere, is used to describe multipolar second harmonic generation from silver metallic nanoparticles. The standard figure of merit of a potential plasmonic sensor based on this principle is then calculated. We finally demonstrate that such a sensor is more sensitive to optical refraction index changes occurring in the vicinity of the metallic nanoparticle than its linear counterpart.