Applications of sub-surface laser engraving on monolithic scintillator crystals: Novel pixel geometries and depth of interaction

Pixelated scintillator crystals are commonly used in gamma radiation detectors. The size of these pixels, the crystal surface treatment and the thickness of the reflector inserted between crystals directly affects energy and spatial resolution as well as the sensitivity of the detector, while increasing the signal to noise ratio by channeling the visible light produced by the gamma photon. Pixel fabrication can be greatly simplified by the application of sub-surface laser engraving (SSLE), where instead of external reflectors, optical barriers are created inside the scintillator itself. Apart from cost effectiveness and ease of application, this technique is free from any geometrical limitations, allowing different shapes or mixed pixel topologies to be used according to the particular application or readout system. In this study we showcase this function by simulating, engraving in LYSO crystal and testing a hexagonal pattern to create the individual pixels. Furthermore, we propose novel concepts of depth-of-interaction, which can be applied on any kind of pixel topologies and demonstrate their behavior in the same hexagonal array. Methodologies to evaluate these designs are also developed and presented. Addition of such characteristics, as well as modulation of light sharing and edge compensation for anger logic readouts is made easily and without any additional overhead, greatly reducing the production cost of a position-sensitive gamma detector.