Monitoring of surface processes with laser-excited surface acoustic waves and dual-probe-beam detection

Abstract
Laser generated broadband surface acoustic wave (SAW) pulses were used for studying surface dynamic processes. The changes in a liquid layer deposited on a Si substrate and the ablation damage of Si wafers were monitored with SAWs. The SAW amplitude, pulse shape and spectrum change after propagation through the area with the liquid layer. These changes can be used for real-time monitoring of the evaporation process and determination of the parameters of the layer. In the laser ablation with a sequence of pulses the etching depth and the extent of the damaged area increase with the number of pulses, affecting transmission of SAWs. A model taking into account dimensions of the ablation groove was developed and used for assessment of the ablation process.