Pulsed laser-target effects and high-resolution process diagnostics

In pulsed laser-target interaction at fluences and fluxes in a range of interest close to the air-breakdown threshold limits, the processes of heating, boiling, melting, chemical decomposition or vaporization occur quasi-explosively. Nonlinear effects due to plasma formation then largely determine the response of the materials. Investigations were carried out at various IR wavelengths (at 2.7 m, 3.8 m and 10.6 m) using a multigas laser (at more than 10 J/pulse) which could be operated as a chemical HF or DF laser and as CO₂ laser in the single-pulse mode. Studies in the repetitively pulsed mode, providing both high peak power densities and rather high average power densities simultaneously, were carried out at =10.6 m with a specially designed multi-kW CO₂ laser system. Both thermal and mechanical effects were studied on dielectric, semiconducting and metallic targets in a large fluence range from several up to hundreds of joules per cm².Valuable insight into the transient phenomena was obtained using fast optical, optronic and electronic techniques. The methods applied, including high-speed photography, videography and laser diagnostics, have proved to be particularly useful for process monitoring or control in industrial laser materials processing applications in order to improve energy transfer rates for optimization purposes.