Improving light extraction from heavy inorganic scintillators by photonic crystals

Abstract

Abstract-The impact of photonic crystal (PhC) slabs on the extraction of light from the heavy inorganic scintillators LuYAP and LYSO is evaluated by combining numerical transmission calculations of a scintillator with PhC coupling face with simulations of the light propagation inside the scintillator. The transmission of the scintillator-PhC coupling face is determined by means of a scattering-matrix algorithm. The PhC slab is assumed to consist of a bulk material with a triangular pattern of air holes that is sandwiched between the scintillator substrate and a layer of optical grease. By folding these data with the angular distribution of the scintillation photons arriving at the coupling face, the light collection efficiency of the system is estimated. The results indicate that a scintillator coupling face equipped with a PhC slab can exhibit a significant gain in . This gain is due to the extraction of photons that are lost in a scintillator with plain exit surface due to total internal reflection. The largest simulated gains of up to a factor of two are observed for small scintillators and for PhC coupling faces with bulk sub , avg sub grease , and , where bulk , sub and grease are the respective refractive indexes of the PhC bulk, the scintillator substrate, and the optical grease, the lattice constant of the PhC pattern, the thickness of the PhC slab, and avg the average refractive index of the PhC slab determined by bulk and the filling factor . Due to the approximations and idealizations of the model, these gains in light collection efficiency may be lower in practical applications and are expected to be achieved only with specular reflectors with reflectivities above 90%, and PhC bulk materials with absorption coefficients abs 10 3 10 4 cm 1 over the whole wavelength range of emission of the scintillator.

Analytical calculation of the lower bound on timing resolution for PET scintillation detectors comprising high-aspect-ratio crystal elements

“…The statistical limit on timing performance showed inverse relationships between the CRLB and the $\sqrt{N}$ and $\sqrt{{\tau }_d}$ dependence for photon statistics and decay time, respectively. This relationship is well known and has been previously reported in [Gundacker et al 2013a, Fishburn et al 2010, Hyman et al 1964, Kronberger et al 2010]. Calculated timing performance was found to improve linearly with SPTR.…”

Time of flight positron emission tomography towards 100ps resolution with L(Y)SO: an experimental and theoretical analysis

“…The photons in our setup are produced with a Cs137 gamma source. Other parameters necessary for photon generation by gamma excitation, like the photo-electric cross section, the gammaabsorption length, and the emission spectrum, were taken from the work of [39].…”

“…Parameters used in our SLITRANI simulation setup. Parameters were taken from the work of [38] and [39]. walls and different contact agents.…”

How Photonic Crystals Can Improve the Timing Resolution of Scintillators

“…We have already shown in [8] that for an emission point in the center of a -mm LSO crystal ( , mm) coupled to a photodetector with silicon grease of , the maximum time spread between the shortest path-length photon, emitted forward along the crystal axis, and the longest path-length photon, emitted backwards at the total reflection angle on the lateral faces, is given by ps (2) not considering multiple reflections on the extraction face. Simulation shows that without a PhC, nearly 50% of the photons are reflected at the first incidence and reappear for several times (if not absorbed) with a delay ranging from 243 and 384 ps times the number of recurrences of the light rays on the coupling face to the photodetector.…”

“…S EVERAL years ago, we identified photonic crystals (PhCs) as a tool with a high potential to significantly improve the performance of scintillator-based detectors [1], [2]. We have shown that well-designed PhCs can enhance the light output of dense scintillators with a high refractive index (between 1.8 and 2.2 for the majority of scintillators) by a large factor ( 2 in air and by at least 50% in grease) [3], [4].…”