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Physics of Excited States in Solids ----- ultrafast laser studies and numerical modeling ----- Olin 209 ------- Qi Li – Ph.D. student Joel Grim – postdoc (WFU ‘12) Yan Wang – Shanghai visiting Keerthi Senevirathne - CEES Burak Ucer – Research Prof. Richard Williams – Prof.

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National Lab Partners Lawrence Berkeley National Laboratory Lawrence Livermore National Laboratory Pacific Northwest National Laboratory Oak Ridge National Laboratory National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation, Office of Nonproliferation Research and Development (NA-22) of the U. S. Department of Energy under Contracts DE-NA0001012 & DE-AC02-05CH11231.

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... ~ 3 nm, ns duration, random location: – not by imaging!

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Particle track 6.1 eV laser Laser experiment 2Δ r ~ µm - mm 1/e for α = 4 x 10 5 cm -1 (NaI) equate e-h densities that produce the same quenching in both cases

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Z-scan nonlinear quenching set-up uv laser PMT integrating sphere translating lens 6 Measuring 2 nd and 3 rd order quenching:

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K 2 = 1 x 10 -9 cm 3 s -1 5.80.30.070.030.30.07 excitation density (e-h/cm 3 ) x 10 20 Quenching is 2 nd order in BGO. Excitons during NLQ.

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K 3 = 8 x 10 -31 cm 6 s -1 3.30.20.060.030.20.06 excitation density (e-h/cm 3 ) x 10 20 Quenching is pure 3 rd order in SrI 2. Free carriers during NLQ.

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Wake Forest data Pacific Northwest National Lab Kinetic Monte Carlo August 2012

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We calculate “electron yield” Y e (E i ) to compare with SLYNCI and K-dip data, by the integral below. F eh (E i,n 0 ) is the fraction of all excitations produced at local density n 0 by an electron of initial energy E i including all delta rays (GEANT4). LLY(n 0 ) is the local light yield model of nonlinear quenching and diffusion in Li et al JAP 2011). Value usedMeasuredMethodReference 0.47 0.35 LY≤1-k 1 Saint-Gobain Dorenbos rev. K 2 (t) (cm 3 t -1/2 s -1/2 ) 0.73 x 10 -15 z-scan 5.9 eV present work K 3 (cm 6 s -1 ) 00z-scan 5.9 eV present work 4 x 10 5 thin filmMartienssen r 0 (nm) 33expt. z-scan/K-dip calc. NWEGRIM WFU, Delft PNNL 10 photocondivity e-pulse Kubota, Brown Aduev 10 -4 10 -4 (STH)STH hoppingPopp & Murray

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k1 = 0.04 LY ≤ (1 - k 1 ) = 0.96 80,000 ph/MeV Cherepy et al Alekhin et al, SCINT LLY of Li et al JAP 2011 with K 3 from z-scan

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Can we measure the radius of an electron track?... phone conversation with Fei Gao (PNNL), Feb. 2012

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Track radius deduced from experiment 50% NaI:Tl K-dip Khodyuk et al NaI:Tl z-scan

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Equating e-h densities, find radius in NaI near track end z-scanK-dip [NWEGRIM, (PNNL) Fei Gao 2012]

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CsI:Tl (0.3%) Induced Absorption

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Qi Li – Young Researcher Award – International Conference on Defects in Insulating Materials, Santa Fe, July 2012. First principles calculations and experiment predictions for iodine vacancy centers in SrI 2

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