Description
Recently, epsilon-near-zero (ENZ) materials have attracted sustainable scientific and technological interest in the fields of advanced photonics and nonlinear optics, offering enhanced light-matter interactions at the nanoscale with promising performance extending from the IR/visible to XUV and hard X-ray ranges. Although some materials with permittivity close to zero exist, most of them are engineered. It is topical to perform their electromagnetic modelling at the wavelength scale to understand their physics and the phenomena occurring within them. We model and numerically analyze plane wave-induced nonlinear intensity-dependent interactions with single and multilayer ENZ nanostructures. In general, the value of permittivity can approach zero both from the positive side, when materials have dielectric properties, and from the negative side, when materials exhibit the properties of metals and plasma. Values of material permittivity that are very close to zero are very sensitive to any changes in the wavelength of the incident radiation, the wavelength of optical wave within material and the amplitude of the electric field of the wave, since this can lead to a sharp deviation in the characteristics of its optical response. When the permittivity approaches zero, the electric field component of electromagnetic wave inside the structures experiences strong enhancement, significantly boosting nonlinear effects. For an ENZ structure with a small initial positive permittivity, the incident wave propagates through the structure with high transmittance. However, even weak defocusing nonlinearity can drive the effective permittivity into the negative value, when the structure has high reflectance. Conversely, for the ENZ structure with a small initial negative permittivity, weak focusing nonlinearity can switch the effective permittivity to a positive value. Thus, by proper controlling intensity of incident electromagnetic wave the self-induced change in the effective permittivity value is possible. As a result, an intensity dependent switching between the transmitting and non transmitting states of the nanostructure can be achieved, demonstrating a robust mechanism for optical switching and limiting in ENZ nanostructures.
