Farell Keiser has been conducting research at Bielefeld University for three years in the Terahertz Physics Group led by Professor Dmitry Turchinovich. A paper by the group has now been published in Physical Review B —with Keiser as first author. The article was also selected as an “Editors’ Suggestion”—an editorial distinction given to only a small number of particularly interesting and significant contributions. First authorship usually identifies the person who made the central contribution to a scientific study. For someone still at school, such first authorship in a leading international physics journal is exceptional.
The research focuses on zinc telluride (ZnTe), which for more than three decades has been one of the most widely used nonlinear crystals for generating and detecting terahertz (THz) radiation with ultrashort laser pulses. THz radiation is used in a wide range of scientific and technological fields—from nanoscience and astronomy to security technology and telecommunications. Keiser observed experimentally that intense laser pulses transiently change ZnTe’s optical properties in the THz range—even under the conditions routinely used for THz generation. He described and characterised these changes using an established theoretical model. The findings enable a more accurate physical description of THz generation in ZnTe.
“Farell did not work on a simplified project specially prepared for a high-school student. He carried out a real experiment, obtained original results, processed the data and made the principal contribution to data analysis and preparation of the manuscript,” says Turchinovich.
In April, Keiser presented the work at the international SPIE Photonics Europe conference in Strasbourg. He received the Best Student Paper Award for his talk, “Transient THz dielectric properties of ZnTe under two-photon excitation”.
Bielefeld University’s “Studieren ab 15” programme enables particularly motivated and high-achieving high-school students to attend regular university courses alongside school, take examinations and earn credits towards a later degree. Keiser has taken this a step further: he is actively involved in experimental research in the group and now publishes his findings in an international journal.
Comment by Professor Dr Dmitry Turchinovich
“Prestigious awards such as the Best Student Paper Award usually go to experienced doctoral researchers. Farell received such an award while he was still at school. The subsequent publication of his article as first author confirms that the prize recognised a substantial piece of scientific work that can be of significant benefit to the wider research community.”
Original publication
Farell Keiser, Wentao Zhang, Dominik Johannesmann, Nicolas S. Beermann, Yuhao Meng, Hassan A. Hafez, Savio Fabretti, and Dmitry Turchinovich: Time-dependent terahertz dielectric function of ZnTe under two-photon optical excitation at 800 nm wavelength. Phys. Rev. B. DOI: https://doi.org/10.1103/myht-1qb7 . First published on 14.10.2026.
Further information
• Bielefeld University’s “Studying at 15” programme
• Professor Dr Dmitry Turchinovich’s research group
Contact
Prof. Dr Dmitry Turchinovich, Bielefeld University
Faculty of Physics
Phone: +49 (521) 106 – 54 68
Email: dmtu@physik.uni-bielefeld.de
Physical Review B
Experimental study
Not applicable
Time-dependent terahertz dielectric function of ZnTe under two-photon optical excitation at 800 nm wavelength.
14-Oct-2026