Analysis of infrared nanojets with self-focusing nonlinearities

Abstract

We present a numerical study of the linear and nonlinear diffraction and focusing properties of dielectric metasurfaces consisting of silicon microcylinder arrays resting on a silicon substrate. Upon diffraction, such structures lead to the formation of near-field intensity profiles that are reminiscent of photonic nanojets and propagate in a similar fashion. The generation and propagation of these photonic jets were analyzed under high intensity mid-infrared illumination conditions for which the third-order optical nonlinearity of silicon leads to pronounced self-focusing effects. The illumination wavelength of 3388 nm was selected to be below the two-photon absorption edge. Our results indicate that the Kerr nonlinear effect enhances light concentration throughout the generated photonic jet with an increase in intensity of about 20% compared to the linear regime for the power levels considered in this work. In all cases, the transverse beamwidth remains subwavelength, and the nonlinear effect reduces the full width half maximum size by 100 nm for both electric field intensity and the longitudinal Poynting vector.