Regensburg 2016 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 3: Optical and nonlinear optical properties, photonic

DF 3.1: Vortrag

Montag, 7. März 2016, 09:30–09:50, H26

Scanning nonlinear absorption in lithium niobate over the time regime of small polaron formation — Holger Badorreck, Stefan Nolte, •Felix Freytag, Pia Bäune, and Mirco Imlau — School of Physics, Osnabrueck University,Barbarastr. 7, 49076 Osnabrueck, Germany

Nonlinear absorption is studied in presence of small polaron formation in lithium niobate using the z-scan technique and ultrashort laser pulses with pulse durations of 70 - 1.000 fs. A model for the analysis of the transmission loss as a function of pulse duration is introduced that considers (i) the individual contributions of two-photon and small polaron absorption, (ii) the small polaron formation time and (iii) an offset time between the optical excitation of free carriers by two-photon absorption and the appearance of small polarons. It is shown that the model allows for the analysis of the experimentally determined z-scan data with high precision over the entire range of pulse durations using a two-photon absorption coefficient of β = (5.6 ± 0.8) mm/GW. A significant contribution by small polaron absorption to the nonlinear absorption is uncovered for pulse durations exceeding the characteristic small polaron formation time of ≈ 100 fs. It can be concluded that the small polaron formation time is as short as (70 - 110) fs and the appearance of small polaron formation is delayed with respect to two-photon absorption by an offset of about 80 fs. Financial support by the DFG (IM37/5-2, INST 190/137-1 FUGG, INST 190/165-1) is gratefully acknowledged. [Baddoreck et al., Opt. Mater. Express 5(12) 2729-2741 (2015)]