Ultrafast laser microprocessing and microwelding

When intense ultrafast laser pulses are focused inside transparent materials such as glass, the optical intensity in the focal area can usually become high enough to initiate the nonlinear optical absorption and then conduct the filamentary propagation of optical pulses. In the filamentary area, plasma is generated due to the nonlinear- and the subsequent avalanche-ionization process, and the material is locally melted and rapidly quenched. Due to this process, microstructure of the material is modified and the refractive index is changed. Especially, in the silica or borosilicate glass, the refractive index usually increases. The positive refractive-index change can be utilized to fabricate various photonic devices, such as waveguides, gratings, and micro lenses inside the materials. One of the applications in the ultrafast laser microprocessing is the microwelding. If the ultrafast laser pulses are focused in the interface between transparent materials, both of the materials can locally be melted and the materials are joined after resolidification. The microwelding technique also allows us to weld transparent and opaque material. The recent experimental results of the ultrafast laser microprocessing and microwelding will be presented.