Light Extraction From Scintillating Crystals Enhanced by Photonic Crystal Structures Patterned by Focused Ion Beam

Abstract

“Photonic Crystals (PhC)” have been used in a variety of fields as a structure for improving the light extraction efficiency from materials with high index of refraction. In previous work we already showed the light extraction improvement of several PhC covered LYSO crystals in computer simulations and practical measurements. In this work, new samples are made using different materials and techniques which allows further efficiency improvements. For rapid prototyping of PhC patterns on scintillators we tested a new method using “Focused Ion Beam (FIB)” patterning. The FIB machine is a device similar to a “Scanning Electron Microscope (SEM)”, but it uses ions (mainly gallium) instead of electrons for the imaging of the samples’ surface. The additional feature of FIB devices is the option of surface patterning in nano-scale which was exploited for our samples. Three samples using FIB patterning have been produced. One of them is a direct patterning of the extraction face of a $0.8\times 0.8\times 10~\hbox{mm}^3$ LYSO crystal. The second and third were ${{\rm TiO}_2}$ coated LYSO crystal with a $1.4\times 1.4~\hbox{mm}^2$ out coupling face partly covered with high-quality photonic crystals. ${{\rm TiO}_2}$ has high refractive index (around 2.1 - 2.4)–which shows the best results in our light extraction simulations. In this paper, SEM images of the samples will be presented together with measurements of excited crystals which show unrivalled performance for such scintillator samples.