Grating-like nanostructures formed by the focused fs laser pulse in the volume of transparent dielectric.

The evolution of optical discharge induced in the volume of transparent dielectric by a focused fs laser pulse is studied under condition of ionization instability that results in deep small-scale periodic modulation of breakdown plasma parameters in the direction of laser polarization. Laser pulse intensity range is found where the instability evolving from very small seed perturbations leads to formation of the contrast subwavelength periodic structure containing narrow zones with overcritical plasma density and enhanced energy deposition. The latter allows considering this structure as underlying the nanograting formation observed experimentally in the fused silica irradiated by series of repeated fs pulses.