Researchers from the University of Rostock and the Max Born Institute in Berlin have demonstrated for the first time that organic crystals – materials made from molecules, such as those found in organic solar cells – can convert short laser pulses into high-energy light. The results were recently published in the prestigious scientific journal Nature Communications.
When very intense laser pulses hit a material, they can move the electrons within it so strongly that light with significantly higher energy is produced. This is known as high harmonic generation. This technique allows researchers to visualize electron movements in materials with unprecedented time resolution in the attosecond range, that is, trillionths of a second. The development of this method earned the 2023 Nobel Prize in Physics, signaling the importance of high harmonic generation for understanding ultrafast dynamics in matter.
Until now, this phenomenon had only been studied in inorganic solids. Now, the team from Rostock has managed to show the same effect for the first time in an organic molecular crystal: pentacene, a material that also plays a key role in organic electronics.
The team, led by Dr. Franziska Fennel, directed ultrashort infrared laser pulses onto thin pentacene crystals in the lab and was able to measure light pulses with up to 17 times the energy of the original laser light. Crucially, this harmonic radiation was very sensitive to the orientation of the crystal and the polarization of the incoming light. This provided a clear indication that even weak interactions between individual molecules play an important role.
Accompanying theoretical simulations showed that this method will enable much more precise investigation of electronic couplings and movements in organic materials in the future – all without the need for electrodes or complex measurement contacts.
"Our work shows that even sensitive organic materials can withstand the extreme conditions of intense laser pulses," explains project leader Dr. Franziska Fennel from the Institute of Physics at the University of Rostock. "This opens the door to a new field of research in which we can make electronic processes in organic semiconductors visible using light pulses."
The study was part of the collaborative research center 1477 “Light–Matter Interactions at Interfaces (LiMatI)” at the University of Rostock and was funded by the German Research Foundation (DFG). In addition to the research groups of Professor Dieter Bauer and Dr. Franziska Fennel at the University of Rostock, researchers led by Dr. Maria Richter from the Max Born Institute in Berlin were also involved.
Publication:
Publikation:
F.-E. Wiechmann, S. Schöpa, L. Bielke, S. Rindelhardt, S. Patchkovskii, F. Morales, M. Richter, D. Bauer & F. Fennel, High-order harmonic generation in an organic molecular crystal, Nature Communications (2025)
Contact:
Dr. Franziska Fennel
University of Rostock
Institute of Physics
Tel.: +49 381 498 6966
E-Mail: franziska.fennel@uni-rostock.de