Exploring the explosive ablation regime of metals in nanosecond micromachining

We present results of single shot ablation experiments for a variety of metal samples (In, Al, Cu, Mo, W, Ti) using visible, nanosecond lasers at fluences up to approximately 10 ⁴ J cm ^-2. At low fluences, usually less than 10 ² J cm ^-2, small amounts of material were removed and removal was approximately uniform across the ablation crater. As the fluence increased above approximately 10 ² J cm ^-2, substantially more material was removed and a conical pit developed in the centre of the ablation crater. The appearance of these conical pits is consistent with material removal by phase explosion mechanisms. In this paper, this ablation phenomenon will be investigated by presenting the crater morphology as a function of fluence. Consequences for micromachining with visible, high repetition rate, nanosecond lasers will be discussed.