SP virtual probe for sensing and imaging biological cells using femtosecond radially polarized beams

Focused femtosecond radially polarized beams were used to excite localized surface plasmons which form a virtual probe on the metal substrate. This was used in the sensing of biological samples in close proximity to the metal and the acquired data was visualized in the form of a local refractive index map. The technique also allows for nonlinear two photon excitation of a fluorescence sample and thus enables concurrent index sensing and multiphoton microscopy.