Structural Changes in Silica Glass by Continuous-Wave Laser Backside Irradiation

We report on a permanent change in the physical properties inside silica glass by rapid heating and quenching using a continuous‐wave laser beam. The absorption of the glass was enhanced by laser heating, and the heated spot moved as a result of thermal radiation and conduction. To trigger heating, an absorbent material was placed on the backside of a glass plate and irradiated through the glass. Laser illumination with a power of 11 W focused on the absorbent material induced a cylindrical modified zone along the laser beam with a length of up to 5.5 mm that was modified at a rate of ∼130 mm/s. The characteristics of the modified silica glass were studied. The modified area consists of two layers, and the diameters of the inner and outer zones are ∼40 and ∼55 μm, respectively. The inner zone was modified by laser heating. The fictive temperature is estimated to be ∼1900 K. The etch rate and hardness of the modified glass increased owing to the increment of the fictive temperature. The outer zone was modified by tensile stress due to the densification of the inner zone. In the outer zone, the etch rate is increased and hardness is decreased.