Laser-induced plasma-assisted ablation of fused quartz using the fourth harmonic of a Nd+:YAG laser

A novel method of micromachining fused quartz by laser-induced plasma-assisted ablation using the fourth harmonic of a Nd+:YAG laser (266 nm) is reported. With the assistance of plasma resulting from laser irradiation on a metal target, the fused-quartz substrate is easily etched by the 264-nm laser beam in spite of the fact that the substrate is transparent to this wavelength. In contrast, no ablation takes place without the metal target, but damage is generated on the substrate surface. The ablated region is observed by optical microscopy and scanning probe microscopy (SPM), which reveal a fine grating structure (line spacing of 20 mu m) without any severe damage. A series of experiments on the dependence of the ablation rate and the threshold laser fluence on ablation parameters, such as laser fluence, the number of pulses, and the distance between the fused quartz and the metal target is performed. On the basis of the results, three possible mechanisms of direct plasma interaction, plasma heating, and metal film deposition are discussed.