**4.3 Nonlinear optics in plasmonic nanostructures**

Metallic plasmonic structure, such as nanoparticle, optical diffraction grating, and nano-aperture, is one well-known and commonly studied method to vastly enhance the efficiency of optical near-field as well as nonlinear optical interactions at the nanoscale, whereas their role is threefold in nonlinear optics; (i) to increase the effect of nonlinearity (ii) to reduce the size of nonlinear components (iii) to have an ultrafast response time, allowing optical signals to be manipulated on

*Nanophotonics: Fundamentals, Challenges, Future Prospects and Applied Applications DOI: http://dx.doi.org/10.5772/intechopen.98601*

**Figure 6.** *An overview of new materials for nanolasers [50].*

femtosecond timescales [53]. In plasmonics, metal dielectric interfaces support surface plasmon polaritons (SPP's) [54], which are p-polarized strongly scattered surface waves associated with oscillations of free electrons in metals, powerful spatial confinement and enhancement in the electric field occur at the interface between the two media following the production of these localized or propagating modes. Owing to the near confinement of the optical field of SPP's, surface effects at metal dielectric interfaces are especially sensitive to variations in the shape of plasmonic nanostructures and the dielectric properties of the embedding optical media. Surface plasmon-polariton modes have been suggested to limit the scale of lasers to sub-wavelength dimensions with the increase of plasmonics. Population inversion of emitters (QD's, fluorophore's) and feedback generated by plasmonic resonant structures are used to achieve lasing in such plasmonic-based structures. The development of new types of nano-resonators and active materials led to the development of a family of nanolasers that drew a lot of interest from the nanophotonics world [48, 50].
