FEMTOSECOND-PULSE VISIBLE LASER PROCESSING OF TRANSPARENT MATERIALS

High-power lasers in industrial and R&D applications raise the general problem of reliability and degradation of optical components. A syste matic study of nonlinear interaction of various transparent dielectric materials as e.g. glasses, fused silica, and polymers, with laser-pul ses in the intensity range of up to 10(13) W cm(-2) is presented. On t he other hand, femtosecond-pulse laser processing in the visible spect ral range (300 fs; 620 nm, similar to 2 eV) allows precise microstruct uring of transparent dielectrics without disruption of the remnant mat erial. Damage and ablation threshold fluences occur above 1.2 J cm(-2) at both silicate glasses and fused silica. Two different photon absor ption mechanisms have been observed. The first occurs during the initi al laser pulses in the incubation range. There, multiphoton absorption results in moderate energy volume densities. These are sufficient to generate morphological changes and optically active defect sites (colo ur centres) which provide a much higher absorptivity relevant fur the second mechanism. It results in gasification without participation of melt.