P. Lecoq CERN 1 October 2012 NSS-MIC Annaheim, October 30th, 2012 How Photonic Crystals can improve scintillator timing resolution Paul Lecoq, E. Auffray, A. Knapitsch CERN, Geneva

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Factors influencing scintillator time resolution Besides all factors related to photodetection and readout electronics the scintillator contributes to the time resolution through: 1.The scintillation mechanism Light yield, Rise time, Decay time 2.The ligh transport in the crystal Time spread related to different light propagation modes 3.The light extraction efficiency (LY  LO) Impact on photostatistics Weights the distribution of light propagation modes P. Lecoq et al, IEEE Trans. Nucl. Sci. 57 (2010) PhC SCINT2013 April Shanghai

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Photonic crystals Crystal Crystal- air interface with PhC grating: θ>θcθ>θc Total Reflection at the interface Extracted Mode θ>θcθ>θc Nanostructured interface allowing to couple light propagation modes inside and outside the crystal air θ>θcθ>θc

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Use large LYSO crystal: 10x10mm 2 to avoid edge effects 6 different patches (2.6mm x 1.2mm) and 1 (1.2mm x 0.3mm) of different PhC patterns 0°45° Photonic crystals A. Knapitsch et al, “Photonic crystals: A novel approach to enhance the light output of scintillation based detectors, NIM A268, pp , 2011

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Measurements: LO angular distribution LYSO: 1.2x2.6x5mm 3

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Motivation1: Improve timing through increased light output Photonic Crystal Slab LYSO 1.2 x 2.6 x 5mm 3 Wrapping + Glue α ph Crystal Air

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Light Transport –-49° <  < 49° Fast forward detection 17.2% –131° <  < 229° Delayed back detection 17.2% –57° <  Fast escape on the sides 54.5% –49° <  < 57° and 123° <  < 131° infinite bouncing 11.1% Improving light extraction efficiency at first hit on coupling face to photodetector is the key

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Photon propagation time spread x L with  1 0  2  c For L = 20mm LSO (n = 1.82) n grease = 1.41   c = 50.8°   t max = 71 ps for x = L  t max = 384 ps for x = 0 Photodetector 

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Motivation2: Improve Timing through redistribution of light propagation modes Regular LYSO Extract more photons at first incidence with PhC = better timing a)b)

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Designed PhC pattern Actual PhC pattern SEM picture Light propagation modes contribution to timing resolution

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Preliminary results 2 PhC configurations tested (P4 & P6) –compared to an unpatterned crystal cut from the same block Small crystal size (1.2x2.6x5mm 3 ) limited by electron beam lithography constrainsts –small sensitivity to light transport variations CTR measurement against a 2x2x10mm 3 LYSO ref. crystal Normalized CTR Normalized LO Ref P4P6 Expected CTR gain for the measured LO gain

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 Towards a nanoimprint mass production technology An 8’’ Si stamp has been produced by UV-lithography and dry etching Direct application of this hard stamp does not give optimal results because of the crystal surface defects Evaluate methods, such as nanoimprint technologies to implement this approach at an industrial scale Intermediate polymer stampPolydimethylsiloxane stamp Si stamp was replicated in two different soft materials to play the role of soft stamp to imprint non- conformal substrate as BGO

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012 First test on BF33 glass substrate  Re-do process with newly polished BGO substrates with a deposited Si 3 N 4 layer from SILSEF

P. Lecoq CERN October NSS-MIC Annaheim, October 30th, 2012Conclusions Photonic crystals improve scintillator timing resolution by two means: –By increasing the light output and therefore decreasing the photostatistics jitter –By redistributing the light in the fastest propagation modes in the crystal Nanoimprint technologies offer attractive solutions for cost effective mass production