Fabrication of finely pitched LYSO arrays using sub-surface laser engraving technique with picosecond and nanosecond pulse lasers

We propose to adopt the sub-surface laser engraving (SSLE) technique for efficient and precise fabrication of finely pitched scintillation crystal arrays. However, its application to thicker crystals is still challenging. It is hard to focus the laser beam tightly at a point far from the crystal´s surface because of the large refractive index of the scintillator. Therefore, a higher laser energy is needed to create microcracks at deep positions in the crystal. Because this would cause excessive damage to the scintillation crystal during laser scans, the process yield of SSLE is reduced. We found that this issue could be overcome by a novel SSLE technique using both picosecond (ps) and nanosecond (ns) pulse lasers. The experimental results indicated that the total laser energy required for creating microcrack walls in a LYSO crystal can be reduced compared to that of conventional SSLE using only a ns pulse laser. The SSLE technique using both ps and ns pulse lasers would enable the fabrication of finely pitched LYSO arrays with a higher process yield.