Laser ablation of Si in water and ambient air

Laser ablation of Si in ambient air and under water is investigated. It is found that the laser ablation rate of Si varies with the thickness of the water layer above the Si substrates. The laser ablation rate is the most highly enhanced with the water layer of 1.1 mm. It is assumed that the plasma generated in water confinement regime (WCR) with an optimal water layer thickness induces the strongest pressure. This high-pressure, high-temperature plasma results in the high ablation rate. A wide-band microphone is used to detect the audible acoustic wave generated during the laser ablation. The amplitude of the acoustic wave is closely related to the ablation rate. It is found that the first peak-to-peak amplitude of the acoustic wave is the strongest when the water layer thickness is 1.1 mm above the substrate. By proper calibration, acoustic wave detection can be used as a real-time monitoring of the laser ablation.