Development of Scribing Technique by using Multiple-laser Beams for Multi-filamentary Coated Conductors

The REBa₂Cu₃O_7-d (REBCO) coated conductors (CCs) with the multi-filamentary structure is very useful for controlling the AC-loss and the shielding current. We have developed laser scribing technique to fabricate multi-filamentary structure by irradiating a rectangular beam using excimer laser source (KrF, λ∼248nm). Since the reflectance of stabilized silver and copper at the wavelength of Nd: YAG or fiber laser (∼ 1 μm) is 98% or more, destructive thermal processing must be required for processing in the wavelength range, which was the reason why we chose the excimer laser as light source. Actually, we successfully fabricated scribing structure with high precision. On the other hand, the improvement of the processing speed has been an important issue to be solved. Although the multi-laser beam system is effective for this purpose, the uniform intensity distribution in the width direction has to be realized. There is no strong Gaussian component in the excimer laser compared with a solid laser. The uniformity is useful for a single beam, however, it is not enough for the multi-beam system. In order to solve this issue, we have modified the beam intensity distribution by using homogenizer. Concretely, the beam intensity in the minor axis direction was flattened by a homogenizer using a plurality of horizontally elongated cylindrical lenses. This modification made the uniform range of laser intensity wider and it was confirmed that multi-laser beams can be applicable as a high-speed scribing technique.