Time-resolved magneto-optics is a well-established optical pump probe technique to generate and to probe spin coherence in semiconductors. By this method, spin dephasing times T_2^* can easily be determined if their values are comparable to the available pump-probe-delays. If T_2^* exceeds the laser repetition time, however, resonant spin amplification (RSA) can equally be used to extract T_2^*. We demonstrate that in ZnO these techniques have several tripping hazards resulting in deceptive values for T_2^* and show how to avoid them. We show that the temperature dependence of the amplitude ratio of two separate spin species can easily be misinterpreted as a strongly temperature dependent T_2^* of a single spin ensemble, while the two spin species have T_2^* values which are nearly independent of temperature. Additionally, consecutive pump pulses can significantly diminish the spin polarization, which remains from previous pump pulses. While this barely affects T_2^* values extracted from delay line scans, it results in seemingly shorter T_2^* values in RSA.
@article{arxiv.1309.6600,
title = {Unambiguous determination of spin dephasing times in ZnO},
author = {Sebastian Kuhlen and Ralph Ledesch and Robin de Winter and Matthias Althammer and Sebastian T. B. Goennenwein and Matthias Opel and Rudolf Gross and Thomas A. Wassner and Martin S. Brandt and Bernd Beschoten},
journal= {arXiv preprint arXiv:1309.6600},
year = {2014}
}