| Arrays of sharp conical spikes are formed on the silicon surface by the cumulative irradiation of ultrashort laser pulses in the presence of ambient gases. The height and space of these sharp conical spikes are on the order of micrometer. The photo absorption of silicon microstructured by ultrashort laser pulses has been enhanced greatly, especially in the infrared region. This novel phenomenon has attracted great interest not only because of the interaction between ultrashort laser pulses and a semiconductor surface, but also because the surface-microstructured silicon absorbs infrared light far more effectively than unpatterned silicon. So the research of the microstructured silicon has great significance both in scientific and in reality.We have constructed the setup used to microstructure silicon surface with ultrashort laser pulses, and systematic studies of the ultrashort laser pulses microstructuring silicon surface were carried out. The formation of the surface microstructures is strongly dependent upon the laser fluence and species of the ambient gases. Sharp conical spikes are only observed in ambient of SF6, while the spikes formed on the silicon surface are much blunt in ambient of N2, air, and vacuum. The height and spacing of these spikes increase with laser fluence.Compared with unpatterned crystalline silicon, the photo absorption of the surface microstructured silicon is significantly enhanced in a wide wavelength range of 0.3～16.7μm. The SF6-prepared surface microstructured silicon shows enhanced photo absorption up to 80% or more in the whole measured wavelength range. The photo absorption of N2-prepared surface microstructured silicon in the wavelength range of 0.25～1.1μm and 9～14μm is about the same as that of SF6-prepared sample, but it decreased to be about 30% in the wavelength range of 3～7μm. Furthermore, photo absorption varies with the height and density of the spikes formed on silicon surface, which indicates that the surface microstructures plays an important role in the enhancement of photo absorption. The photo absorption of metal film coated on surface microstructured silicon was also investigated.We have also fabricated a prototype photovoltaic device based on the surface microstructured silicon to study its photovoltaic properties. Under the illumination of Helium-Neon laser at 632.8nm, the open-circuit voltage (Voc) and short-circuit current (Isc) of the prototype device were measured to be 53.3 mV and 0.11 mA, respectively at a maximum power conversion efficiency of 1.44%. Upon excitation with Helium-Neon continuous laser at 632.8 nm, external quantum efficiency (EQE) of surface microstructured silicon as high as 112.9% has also been observed. The current-voltage characteristic and photo responsivity of the prototype photovoltaic device were also investigated.femtosecond laser pulses irradiation of metallic bulk crystal of Au (110) was experimentally studied. Three irradiation regimes were found in terms of laser fluence. Several intriguing results are found from these experiments:(1) novel surface waves were created only for laser irradiation fluences below 1 J/cm2, whose period can not be predicted by Rayleigh's diffraction condition. (2) For laser fluences above 5 J/cm2, surface wave effect on morphology disappeared, just grains could be observed. (3) For laser fluences between 1.5 J/cm2 and 4 J/cm2, laser induced period surface structures (LIPSS) appeared under the irradiation of femtosecond laser pulses. A previously unobserved laser-induced novel surface wave formation phenomenon was observed for Au foil surface in the region of low laser fluences.
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