Optical linear and third-order nonlinear properties of nano-porous Si

In this paper, we present a systematic experimental study of effective optical linear refractive index and third-order optical nonlinear effective susceptibility of nano-porous silicon samples with various values of silicon volume fill fractions. The experimental results are in good agreement with the theoretical predictions of our simplified Bruggeman formalism for effective optical linear and third-order nonlinear susceptibilities, which was previously presented. We derived the effective linear refractive index from measurements of the nano-porous silicon reflectivity. For the third-order optical nonlinearities measurements, we used the reflection intensity scan method. A new relation for the dependence of third-order effective nonlinear optical susceptibility on the silicon volume fill fraction (for nano-porous silicon samples with silicon volume fill fraction ≤ 0.5) and on measured nonlinear reflections (at λ = 633 nm) is derived and used to get the effective third-order nonlinear susceptibility.