Characterization of thin layers using a frequency domain laser-ultrasonic system

We characterize the elastic and geometric properties of thin coatings by measuring the dispersion curves of surface acoustic waves. The used laser-ultrasonic system generates single frequency surface acoustic waves with a modulated continuous wave laser source. In contrast to pulsed laser excitation this technique avoids high peak powers and broadband detection, enabling non-destructive characterization of sensitive coatings. In addition to temporal modulation we apply spatial modulation to the excitation beam amplitude, which drastically decreases the power density on the sample surface and enables a direct determination of dispersion relations.