Berlin 2015 – scientific programme

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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 c_OH⁻ ≈ 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.