ANISOTROPIC INFRARED-UP-CONVERSION LUMINESCENCE GENERATION IN POROUS SILICON

It is demonstrated in this paper that the infrared-up-conversion luminescence generation from porous silicon, considered as an enhanced third-order nonlinear optical effect by the recent work, is anisotropic as the polarization vector of normally incident fundamental light is rotated. A new method has been used to determine the anisotropy parameter \sigma of the third-order nonlinear optical tensor \chi⁽³⁾. Due to the sensitivity of \sigma to the crystal structure and microscopic electronic properties, the difference in \sigma′s between porous and crystalline silicon, particularly in their phases, demonstrates that the nanometer structure of porous silicon induces a dra-matic change of the electronic band structure, but the strongly anisotropic crystal property remains unchanged.