VUV-UV multiwavelength excitation process using F2 and KrF excimer lasers

VUV-UV multiwavelength excitation process for precision microfabrication of hard materials, in which simultaneous irradiation of the vacuum ultraviolet (VUV) laser beam with extremely small laser fluence and the ultraviolet (UV) laser beam leads to effective ablation, is reviewed. A collinear irradiation system of F2 and KrF excimer lasers has been developed for this process. This system achieves well- defined micropatterning of fused silica and GaN with little thermal influence and little debris deposition. Ablation mechanism is explained as absorption of KrF excimer laser by excited-states formed by F2 laser (excited-state absorption: ESA). In addition, this technique is applied for much more efficient refractive index modification of fused silica compared with single F2 laser irradiation, which is attributed to resonance photoionization-like process based on ESA. These processes are characterized by experiments carried out at various conditions such as laser fluence, irradiation timing of each laser beam, and pulse number.