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Abstract
We present an experimental investigation into the third-order nonlinearity of conventional crystalline (c-Si) and porous (p-Si) silicon with Z-scan technique at 800-nm and 2.4- μ m wavelengths. The Gaussian decomposition method is applied to extract the nonlinear refractive index, n 2 , and the two-photon absorption (TPA) coefficient, β , from the experimental results. The nonlinear refractive index obtained for c-Si is 7 ± 2 × 10 − 6 cm 2 /GW and for p-Si is − 9 ± 3 × 10 − 5 cm 2 /GW. The TPA coefficient was found to be 2.9 ± 0.9 cm/GW and 1.0 ± 0.3 cm/GW for c-Si and p-Si, respectively. We show an enhancement of the nonlinear refraction and a suppression of TPA in p-Si in comparison to c-Si, and the enhancement gets stronger as the wavelength increases.
Highlights
Porous silicon (p-Si) has attracted great interest in recent years due to its unique opto-electronic properties
We show an enhancement of the nonlinear refraction and a suppression of two-photon absorption (TPA) in p-Si in comparison to crystalline silicon (c-Si), and the enhancement gets stronger as the wavelength increases
The information on p-Si nonlinearity remains scarce, and our work attempts to form a clearer understanding of the topic through investigating the self-focusing and two-photon absorption (TPA) processes
Summary
Porous silicon (p-Si) has attracted great interest in recent years due to its unique opto-electronic properties. The nanoscale sponge-like structure of p-Si, whereas porosity significantly enlarges its surface-to-volume ratio, exhibits the quantum confinement effect [1], resulting in faster carrier recombination [2], accompanied, at certain conditions, by photo-luminescence [3] and optical nonlinearities [4]. These effects are usually greatly enhanced in comparison to the conventional crystalline silicon (c-Si). The information on p-Si nonlinearity remains scarce, and our work attempts to form a clearer understanding of the topic through investigating the self-focusing and two-photon absorption (TPA) processes. We employed the Z-scan technique using 800-nm and 2.4-μm femtosecond laser beams
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