In-process debris removal in femtosecond laser processing

Abstract

Debris deposited around laser-processed structures, which is a critical issue in high-precision laser processing, should be removed. A new method for laser cleaning of debris was developed. A glass surface was irradiated with a line-focused beam for laser cleaning, together with a focused beam for laser processing. Both beams were formed by computer-generated holograms (CGHs) displayed on a spatial light modulator. The distance between the two beams was controlled with the CGHs, and the time difference was controlled with an optical delay line. These optical structures were the novel aspect of our laser processing system. When two beams were superposed at the same position on a sample, we did not find a suitable beam parameter for debris removal, but we found that the processing area was spatially enlarged depending on the temporal overlap. In contrast, when two beams separated by an adequate distance were radiated on a sample, we found suitable beam parameters for debris removal. Debris removal was effectively performed when the scanning speed of the laser beams was low, because the low scanning speed produced a temperature higher than the glass transition temperature, and the heated and melted debris was ablated due to a smaller ablation threshold than that of the glass substrate. This in-process laser debris removal method has the advantages of needing no additional equipment other than the optics, no additional operations, no special materials, and no specific operating environment.