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DF: Fachverband Dielektrische Festkörper
DF 11: Small Polarons in LiNbO3
DF 11.10: Talk
Wednesday, March 18, 2015, 12:40–13:00, EB 133C
Light induced changes in the OH−-stretching bond by frequency-resolved femtosecond infrared absorption spectroscopy in congruent LiNbO3 — •Felix Freytag, Phillip Booker, and Mirco Imlau — Department of Physics, Osnabrueck University, D-49069 Osnabrueck
The light induced generation of polarons in LiNbO3 is well studied by observing the absorption changes in the VIS/NIR spectral range. However, time-resolved measurements of the generation and relaxation of polarons in the MIR spectral range are missing. LiNbO3 crystals contain defects from OH−-ions with a concentration of cOH− ≈ 1018 cm−3. Due to protons coupling these ions attach to the O2−-ions in the lattice at four different positions [Lengyel et al., Ferroelectrics 257, 255 (2001)]. Polarons change the enviroment of OH−-Ions an therefore their vibrational resonance. Here we show data of a frequency-resolved femtosecond infrared spectroscopy experiment of the OH−-stretching bond (λ ≈ 2870 nm) in congruent LiNbO3 consisting of four components (due to slightly different positions in the crystal lattice). The transmission of mid-infrared pulses (τ ≈ 230 fs) is detected by two multichannel HgCdTe detectors as a function of a variable time delay to an intense VIS pump pulse of τ ≈ 100 fs duration. We discuss the light-induced changes in the optical density of the OH−-stretching bond. Financial support by the DFG (IM 37/5-2, INST 190/165-1 FUUG) is gratefully acknowledged.