We report on a medium exhibiting extremely efficient light scattering properties: a liquid network formed in a porous matrix. Liquid fragments confined in the solid matrix result in a random fluctuation of the dielectric function and act as scattering objects for photons. The optical scattering efficiency is defined by the filling factor of the liquid in the pores and its dielectric constant. The spectral dependence of the scattering length of photons indicates that the phenomenon is governed by a Mie-type scattering mechanism. The degree of the dielectric disorder of the medium, i.e. the level of opacity is tunable by the ambient vapor pressure of the dielectric substance. In the strongest scattering regime the scattering length of photons is found to be in the micrometer range. By incorporation of dye molecules in the voids of the porous layer a system exhibiting optical gain is realized. In the multiple scattering regime the optical path of diffusively propagating photons is enhanced and light amplification through stimulated emission occurs: a strong intensity enhancement of the dye emission accompanied by significant spectral narrowing is observed above the excitation threshold for a layer being in the opalescence state.
We report on a strong intrinsic optical anisotropy of silicon induced by its dielectric nanopatterning. As a result, an in-plane birefringence for nanostructured (110) Si surfaces is found to be 10<sup>5</sup> times stronger than that observed in bulk silicon crystals. A difference in the main values of the anisotropic refractive index exceeds that one of any natural birefringent crystals. The anisotropy parameters are found to be strongly dependent on the typical size of the silicon nanowires assembling the layers. The value of birefringence is dependent also on the dielectric surrounding of silicon nanoparticles assembling these layers. We show that stacks of layers having alternative refractive indices act as a distributed Bragg reflectors or optical microcavities. Dichroic reflection/transmission behavior of these structures sensitive to the polarization of the incident linearly polarized light is demonstrated. These findings open the possibility of an application of optical devices based on birefringent silicon layers in a wide spectral range.
We report on a strong intrinsic optical anisotropy of silicon induced by dielectric nanopatterning. As a result, in-plane birefringence of anisotropically nanostructured (110) oriented Si is found to be 10<sup>5</sup> times larger than that observed in bulk silicon. The difference of the main values of the anisotropic refractive index (Δn) exceeds that of any natural birefringent crystal. Δn depends strongly on the typical size of the silicon nanowires assembling the layers and the dielectric constant of the medium surrounding these silicon nanoparticles. We show that dielectric stacks of anisotropically nanostructured Si can act as a dichroic distributed Bragg reflectors or optical microcavities. The reflection/transmission behavior of these structures is sensitive to the polarization of the incident linearly polarized light. These findings open the possibility of an application of optical devices based on birefringent silicon layers in a wide field.