Direct imaging of the fragments produced during excimer laser ablation of YBa₂Cu₃O_7-δ

The evolution dynamics of the fragments produced during KrF excimer laser (248 nm, 25 ns) ablation of YBa2Cu3O7-δ has been observed by ultrafast photography using a synchronized dye laser beam (∼1 ns) to probe above the target surface. The images show that fragment removal is initiated near the beginning of the laser pulse (≳10 ns), continues for a maximum of a few hundred nanoseconds, and has an expansion front velocity suggesting a target temperature varying from about 1500 to 4000 K or greater. The shock wave formed due to interaction of the ablated fragments with background oxygen gas has also been photographed, and its temporal evolution as a function of oxygen pressure has been shown to agree better with a planar than spherical model. The overall picture is that of an ablation process showing pronounced but understandable gas-dynamic effects.