Nanogratings in Fused Silica: Structure, Formation and Applications

Abstract

We investigate the formation of periodic subwavelength structures, so-called nanogratings , in the volume of fused silica. These self-organized structures emerge upon irradiation with ultrashort laser pulses at intermediate intensities. Using Small Angle X-ray scattering and Focused Ion Beam milling we could prove that they consist of hollow cavities, whose arrangement give rise to the overall periodicity. The formation of the grating structure undergoes three distinct stages of growth from initially randomly distributed nanostructures to extended domains with uniform periodicity after several hundreds of laser pulses. The experiments revealed that the cumulative action of subsequent laser pulses is mediated by dangling-bond type defects. On shorter time scales, transient self trapped excitons may significantly enhance the formation process. The periodic subwavelength structure of nanogratings leads to form birefringence, which can be utilized to implement optical functionalities. Wave plates based on nanogratings offer a great deal of flexibility and precision regarding their retardation as well as the orientation of their optical axis.