Metamaterials: Nonlinear Optics And Its Applications

Metamaterials, as a new type of artificial material, have brought about new progressin scientific researches from the beginning of21st century. Different from natural ma-terials, the presence of surface plasmon polaritons （SPP） inside metamaterial, formedby coupling between photons and electrons, will lead to different optical properties.Extending from demonstration of negative refractive index since2000to successfullycloaking of objects, metamaterials brought surprises continuously, and provided per-fect material platform for realizing any fancy of human beings. On the other hand, thegeneration of SPP inside metamaterials results in localization of electromagnetic ener-gy in a space with sub-wavelength dimensions, in which the energy density is highlyincreased, hence with stronger interaction between electromagnetic field and materials.In this thesis, we will introduce how to utilize the electromagnetic energy localizedby SPP to enhance the third order nonlinear absorption of asymmetric split ring （ASR）metamaterials. We managed to achieve40%decrease in transmittance of metamate-rial with50nm thickness only under peak laser irradiation intensity of2.3GW/cm².The nonlinearity enhancement behavior could be explained by effective nonlinear en-hancement theory. The pump-probe experiment was also adapted to study the temporaldynamics properties of the metamaterial, which gives sub100fs response time, pavingthe way for realizing optical signal processing system with terahertz bandwidth in thefuture. At last we will discuss the potential applications of our metamaterials in thearea of optical switching, optical limiting and mode locking.Based on this, in chapter3, we will move to giant nonlinear extrinsic chiral opticalactivity effect in our metamaterial. Among all of the properties of optical wave, itspolarization has drawn a lot of attention, since it is related to the spin momentum ofphoton, controlling of which is extremely meaningful in realizing future quantum com-munication system. In1979, Akhmanov successfully observed the nonlinear opticalactivity effect from LiIO₃crystals, however, due to its weak response (nonlinear spe-cific rotation～10^-11°cm/W), the application is quite limited. The discovery of giant nonlinear optical activity inside ASR metamaterial makes it possible to rotate polariza-tion plane by more than1just under2GW/cm2peak intensity, leading to nonlinearspecific rotation with3×10^-4°cm/W, which is30million times larger than LiIO₃crystals. It provides the possibility of realization of nonlinear controlling or switchingof optical wave polarization and is fundamental in building quantum communicationsystem.The photoluminescence properties of ASR metamaterials are going to demonstrat-ed in chapter4. Intuitively, the emission wavelength, i.e. the color of light emitted frommaterial is determined by the energy structure of themselves. Super-lattice opened theway of modifying the energy band structure of material, making it possible to cover thewhole spectral range from visible to infrared. It will be shown that by changing the statedensity spectral distribution of photons inside metamaterials, the spontaneous lumines-cence spectra of metamaterials will be modified according to Purcell effect. Throughchanging the structure parameters of metamaterials, we managed to control the positionof emission peak and polarization state of luminescence emission from metamaterials.