Effect of liquid thickness on laser ablation efficiency

The purpose of this study was to investigate the effect of liquid thickness on laser ablation efficiency. Both Q-switched Nd:YAG (yttrium aluminum garnet) and free-running Er:YAG lasers were used to ablate polymethyl-methacrylate samples in the presence of a water layer. The thickness of the liquid layer varied from 500μmto3mm. Ablation performance as a function of liquid thickness for both lasers was quantitatively measured by optical coherence tomography. For the Q-switched Nd:YAG laser, wet ablation produced up to three times greater ablation volume than dry ablation, and the ablation efficiency decreased with increase of liquid thickness. On the other hand, for the Er:YAG laser, wet ablation with a 500μm layer of water produced comparable ablation volume to dry ablation. Ablation performance decreased as the liquid layer thickness increased. Q-switched laser ablation assisted by a thin liquid layer efficiently augmented material removal, while ablation efficiency of a long-pulsed Er:YAG laser decreased as water thickness was increased.