G. Herziger

Dynamics of laser processing in transparent media

High-quality laser processing for industrial production requires, in addition to a suitable beam source, an appropriate adaption of the laser emission to the processing material. Therefore the interaction of the high-intensity laser beam with solid transparent matter was investigated. The kinetics of heating and evaporation by laser pulses was studied. The experiments showed that transparent materials can be vaporized by laser light in spite of their small absorption. The first initial spike (peak intensity \sim10^{8} W/cm2) turns the absorption coefficient of a surface layer in a very short time ( \sim10^{-7} s) from 10-2to 103cm-1. The further emission is absorbed completely in the heated layer and vaporizes the material at an approximately constant rate. A model explaining the heating of transparent materials by laser beams is demonstrated and accounts for the experimental observations. The shape of the resulting holes is discussed.

Interferometrisches Verfahren zur Registrierung von Bruchgeräuschen in glasfaserarmierten Kunststoffen

ZusammenfassungIn glasfaserarmierten Kunststoffen treten beim Reissen von Fasern oder Lösen der Fasern vom Bindemittel schwache Bruchgeräusche auf. Diese rufen als Sekundäreffekte stark gedämpfte Oberflächenschwingungen des Werkstückes hervor. Die Schwingungen können durch Analyse des zeitlichen Verhaltens der Interferenzstreifen in einer interferometrischen Anordnung empfindlich nachgewiesen werden.AbstractIn armored synthetic materials fracture noise is appearing if single fibres are breaking up or are separated from the bound material. This process gives rise to strong damped surface oscillations of the synthetic material. The amplitude and frequency of this oscillation can be detected with high sensitivity by an analysis of the time behaviour of the interference pattern in a interferometric experimental arrangement.

Laser spiking to control material processing

Approximate theoretical solutions describing the spiking behaviour of solid state lasers are compared with experimental results at high power levels. In agreement between theory and experiment the spike pattern can be easily controlled by external laser parameters. Due to its reproducibility and simplicity this technique is well suited to adapt the laser emission to the kinetics of laser machining which is strongly depending on the kind of processing and material.ZusammenfassungEs werden Näherungslösungen für das Einschwingen von Festkörperlasern mit experimentellen Resultaten im Bereich hoher Laserleistungen verglichen. Übereinstimmend mit den theoretischen und experimentellen Ergebnissen kann der Einschwingverlauf durch geeignete Wahl der Laserparameter gesteuert werden, Damit ist es möglich, den Laser den verschiedenen Anforderungen anzupassen, die bei der Materialbearbeitung auftreten.