Nonlinear Plasmonics

We study the optical response of metal nanoparticles under the illumination of high-power ultrashort laser pulses. The term "ultrashort" means, that the pulse duration of the laser pulses is on the order of femtoseconds (10^-15s) and these generate when focused onto the nanostructures light intensities in the ~10 GW/cm² range. When such an intense light beam interacts with matter the enormous light intensities lead to a plethora of new phenomena, which we usually do not observe in every day experience, since e. g. sunlight propagating through a glass window simply does not deliver the necessary electric fields strength. In particular, the new nonlinear optical effects lead often to the generation of new frequency components (colors) of the propagating laser beam. The most famous phenomena are probably "Second Harmonic Generation" (SHG) or "Third Harmonic Generation" (THG). In SHG for example two incoming photons are combined via the light-matter interaction into one outcoming photon of twice the energy of the incoming photon. This effect is very often used for green laser pointers, where actually an infrared laser at a wavelength of 1064nm is frequency doubled in a nonlinear optical crystal to a wavelength of 532nm, which corresponds to green color.