Anisotropy of infrared-upconversion luminescence generation in porous silicon

Abstract

It is demonstrated that the infrared-upconversion luminescence generation from porous silicon, which was considered as an enhanced third-order nonlinear optical effect in our recent work, is anisotropic as the polarization vector of normally incident fundamental light is rotated. A new method was used to determine the anisotropy parameter σ of the third-order nonlinear optical tensor ${\mathit{X}}^{\mathrm{}\left(3\right)\mathrm{}}$. Due to the sensitivity of σ to the crystal structure and microscopic electronic properties, the difference of σ between porous silicon and crystalline silicon, particularly of their phases, demonstrates that the nanometer structure of porous silicon induces a dramatic change of the electronic band structure, but the strong anisotropic crystal property remains.