Femtosecond and nanosecond laser fabricated substrate for surface-enhanced Raman scattering

We report a simple and repeatable method for fabricating a large-area substrate for surface-enhanced Raman scattering. The substrate was processed by three steps: (i) femtosecond (fs) laser micromachining and roughening, (ii) thin-film coating, and (iii) nanosecond laser heating and melting. Numerous gold nanoparticles of various sizes were created on the surface of the silicon substrate. The 3D micro-/nanostructures generated by the fs laser provide greater surface areas with more nanoparticles leading to 2 orders of magnitude higher of the enhancement factor than in the case of a flat substrate. Using an He-Ne laser with a 632.8 nm excitation wavelength, the surface-enhanced Raman scattering enhancement factor for Rhodamine 6G was measured up to 2×10(7).