Laserakustik für Schicht- und Oberflächenprüfung

A laser-acoustic test method is presented, which can be used for the non-destructive characterization of coatings and material surfaces. The method measures the dispersion of surface acoustic waves induced by short laser pulses. The technique is based on the fact that the propagation velocity of the wave depends on the frequency in coated and surface modified materials. Measuring the dispersion of the surface acoustic wave enables to determine important properties of the material surface. Three examples demonstrate that the laser-acoustic method can solve very different problems of surface engineering. The wear resistance of diamond-like carbon film with a thickness of few nano-meters was evaluated. The elastic modulus of thermally sprayed coatings which are typically some hundred micro-me ters thick was measured, which allows to conclude on the defect structure of the coatings. The depth of sub-surface damage layers in semi-conductor materials was determined, which are created when the wafer is sliced from the ingot.