Control of Periodic Nanostructure Embedded in SiO2 Glass under Femtosecond Double-Pulse Irradiation

The polarization-dependent periodic nanostructure are successfully induced by the femtosecond double-pulse train. Such nanograting structures consist of periodic modulation of oxygen deficiency with nanoscale. Furthermore, we have also observed that this stripe-like oxygen defect regions include nanopores. Additionally, the average size of the induced nanopores by the double-pulse train was twice as large as that of the single-pulse train, despite of the same total energy. As the results, twice higher birefringence can be obtained by the double-pulse train irradiation.