How photonic crystals can improve the timing resolution of scintillators

Abstract

Photonic crystals (PhC) and quantum optics phenomena open interesting perspectives to enhance the light extraction from scintillating media with high refractive indices as demonstrated by our previous work. By doing so they also influence the timing resolution of scintillators by improving the photostatistics. The present contribution will demonstrate that they are actually doing much more. Indeed photonic crystals, if properly designed, allow the extraction of fast light propagation modes in the crystal with higher efficiency contributing therefore to increase the density of photons in the early phase of the light pulse. This is of particular interest to tag events at future high-energy physics colliders, such as CLIC, with a bunch-crossing rate of 2 GHz, as well as for a new generation of Time of Flight Positron Emission Tomographs (TOFPET) aiming at a timing resolution of 100ps. At this level of precision a good control of the light propagation modes is essential if we consider that in a 2×2×20m m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> LYSO crystal, the time spread (peak to peak) of extracted photons can be as large as 400ps considering simple bouncing only. The paper presents a detailed analysis of the light propagation and extraction modes in a LYSO crystal combining the LITRANI light ray tracing and the CAMFR PhC simulation codes. Ongoing measurement results are shown with an attempt to unfold the contribution from the improved photostatistics resulting from the total enhanced light output on one side and from the improved contribution of fast propagation modes extraction on the other side. Some results are also shown on a new and more industrial process to produce PhCs by the use of nanoimprint technology.