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

Abstract

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.

Design and Performance Study of a Quasi-spherical PET Scanner and Hexagonal SiPM

“…The energy and power density values are in the range of previous works in the field with nanosecond laser [145].…”

“…It could be considered though the combination of ultrashort pulses in the range of picoseconds to induce multi-absorption process and create small plasma balls of high absorption and a subsequent nanosecond pulse to finally induce the damage by thermal stress. This has been satisfactory proposed [145].…”

“…Subsequently, fewer energy deposition derived in precise ablation or bulk material alteration. The combination of picosecond and nanosecond pulses to induce controlled damage has been already proposed [145]. They reported refined engraving by first inducing an absorber with the picosecond pulse and subsequently produce thermal expansion and strain with nanosecond pulse that eventually results in a microcrack.…”

“…Another doable alternative is the application of material laser processing to imprint scintillation blocks with the desired discrete pattern [144][145][146]. Briefly explained, the electric field of the laser's wave and the high achievable irradiance of lasers, beyond 10 10 W/cm 2 , can drive the crystal lattice into vibration that it is eventually transmitted around the solid by linking of molecules.…”

“…The flexibility in the engraving position, geometry and density of the SSLE technique has been exploited in different designs. Several authors have revised the common square grid with pitch of 2 mm [148,149], 1.2 mm [145] and 0.8 mm [146]. Non-square honeycomb tiling has been also proposed [150].…”