Electron Density Estimation and Fiber Fuse Simulation in Laser-Irradiated Bulk Glass

Abstract

To clarify the formation mechanism of periodic nanometer-size cavity structure of a borosilicate glass sample, the free electron density around the exit surface was investigated when it exposed to intense femtosecond laser radiation. The electron density near the edge of the crack on the surface was estimated to be 10 20 -10 22 cm -3 . From this result, the temperature of the irradiated heating area near the edge of the crack was estimated to reach at least about 6,000 K, which was sufficient for the initiation and propagation of the fiber fuse. In this way, periodic nanosized cavities could be formed by fiber fuse propagation starting near the edge of the crack on the exit surface. Next, fiber fuse propagation in the modified zone formed by continuous-wave laser irradiation in a silica glass sample was investigated theoretically by the explicit finite-difference method using the thermochemical SiO x production model. In the calculation, we assumed the glass to be in an atmosphere and that part (40 µm in length) of the modified zone was heated to a temperature of 2,923 K. The calculated velocities of fiber fuse propagation in the modified zone were in fair agreement with the experimental values observed at 0.514 and 1.064 µm.