Linear and nonlinear optical anisotropy of amorphous oxidized silicon films induced by a network of pores
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By thermal oxidation of initially birefringent porous silicon, highly optically transparent films of porous silicon oxide are produced. These films exhibit strong in-plane birefringence, which is twice as high as that of crystalline quartz. The experimentally measured refractive indices for ordinary and extraordinary waves in oxidized porous silicon are explained in terms of an effective-medium model by taking into account the form anisotropy of preferentially oriented pores in a silicon oxide matrix. The third-harmonic generation efficiency studied as a function of the pump wavelength suggests that the form birefringence of porous silicon oxide films can be used to phase match the nonlinear optical interactions. 2006 The American Physical Society.