Time-resolved axial-view of the dielectric breakdown under tight focusing in glass

We present time-resolved studies of the dielectric breakdown using tightly focused femtosecond (fs) laser pulses in glass. Axial evolution of the breakdown and material modifications have been retrieved over the time span from 0 to 1 ns with a 50 fs resolution and ∼ 1 μm spatial resolution using interferometric pump-probe technique. It is shown that even at pulse power slightly above critical Pcr ≃ 1 MW/pulse, the filamentation was limited at tight focusing and the central focal region with resolidified glass was localised axially within ∼ 10 μm; it can be used for the waveguide recording. Mechanisms of light-matter interaction at tight focusing and application potential are discussed. The electron-ion scattering time, τe–i ≃ 1.1 fs, for the glass at electron concentration ne ≃ (4–5)×1020 cm−3 was determined within Drude approximation.