Formation of Si nanocrystals in glass by femtosecond laser micromachining

We report on the precipitation of Si nanocrystals inside a borosilicate glass by using an 800 nm, 250 kHz femtosecond laser irradiation, which was confirmed with X-ray diffraction, Raman spectra and transmission electron microscopy analyses. Refractive index profile reveals that the refractive index of the Si nanocrystals precipitated region increased up to 8.7% in comparison with that of the unirradiated area, leading to a large diffraction efficiency of the fabricated dot structure. Furthermore, the third-order optical nonlinearity of the Si nanocrystals precipitated glass is greatly enhanced based on the Z-scan measurement. These results may find applications for the fabrication diffractive optical devices and optical switches. Crown