| Popis: |
Irradiation of metals with ultrashort laser pulses reveals a variety of versatile microscopic processes compared to longer pulses. In particular, the impact of some material-specific characteristics, such as the electron-phonon coupling, seems to get more significance in order to meet the machining requirements. Finding the optimal process parameter area has been therefore a dominating problem in materials processing with sub-picosecond laser radiation. Ablation of bulk metals (Al, Cu) has been investigated in-situ by means of high-resolution pump-probe photography using pump laser radiation of pulse duration t p =80 fs, at wavelength of 820 nm. This technique enables direct visualization of laser-induced processes up to 1 μs after the interaction of a single laser pulse with material. Variation of the fluence of the laser radiation, behavior and time characteristics of melting and post-melting processes have been matter of research. Depending on metal-specific parameters, qualitatively different ablation phenomena have been observed. Structural analysis by electron and optical microscopies reveals rosette-like surface structures showing the morphology of the ablated regions. The temporal development of the ablation dynamics can be conditionally categorized into different characteristic time regions. Particularly, laser induced melt injection has been observed in the time range of 700 ns to 1.0 μs after the initial laser-metal interaction. |
