The paper reports the observation of self-organized periodic nanostructures in silica glass after irradiation with intense femtosecond light pulses from a Ti:sapphire laser. These structures, consisting of striplike regions with a low oxygen concentration, are aligned perpendicular to the laser polarization direction and have a width of about 20 nm. The period of these structures can be controlled by adjusting the pulse energy and the number of pulses. The phenomenon is interpreted as the result of interference between the incident light field and the electric field of the bulk electron plasma wave, leading to periodic modulation of electron plasma concentration and structural changes in the glass. The study provides the smallest embedded structures ever created by light and has potential applications in optical recording and photonic crystal fabrication.The paper reports the observation of self-organized periodic nanostructures in silica glass after irradiation with intense femtosecond light pulses from a Ti:sapphire laser. These structures, consisting of striplike regions with a low oxygen concentration, are aligned perpendicular to the laser polarization direction and have a width of about 20 nm. The period of these structures can be controlled by adjusting the pulse energy and the number of pulses. The phenomenon is interpreted as the result of interference between the incident light field and the electric field of the bulk electron plasma wave, leading to periodic modulation of electron plasma concentration and structural changes in the glass. The study provides the smallest embedded structures ever created by light and has potential applications in optical recording and photonic crystal fabrication.