‘Optoelectronics based on new types of semiconductors, devices, and the phenomena that occur within them, is only nascent. There are still many perplexing problems we need to solve,’ says Prof. Tomasz Czyszanowski, who collaborates with leading scientists from around the world on a daily basis.
Publication in Nature Photonics
The paper Bose-Einstein Condensation of Photons in a Vertical-Cavity Surface-Emitting Laser was co-authored by dr hab. Maciej Pieczarka, the project’s originator, and Aleksandra Piasecka from Wroclaw University of Technology, who conducted the experimental research reported on in the paper. The researchers from Lodz University of Technology also played a key role. Dr Marcin Gębski, along with Prof. James Lott from Technische Universität Berlin, fabricated the lasers used in the experiments. Furthermore, dr hab. Michał Wasiak, university professor, and Prof. Axel Pelster from Technische Universität Kaiserslautern-Landau contributed to the theoretical analysis of the experimental results. Prof. Tomasz Czyszanowski performed the computer simulations that helped interpret these findings.
The findings
‘Nature Photonics publication shows that photons generated by a laser that differs slightly from relatively conventional semiconductor lasers – such as those used in telecommunications and LIDAR systems – behave like a gas of non-interacting particles that can reach a Bose-Einstein condensation state. No one before us has managed to prove that such a phenomenon is possible in an electrically-powered semiconductor laser operating at room temperature,’ explains Prof. Czyszanowski. In previous experiments, this phenomenon was only observed in complex optical systems built on large optical tables and not by a laser small enough to fit on the tip of a needle.
The researchers identified the key properties of photons emitted by such lasers. As explained by Prof. Czyszanowski and Prof. Wasiak:
‘Imagine that photons in a laser occupy different rungs on a ladder, where each rung corresponds to an allowed photon energy level. In the semiconductor lasers we are studying, the distribution of photons across these rungs is uneven and seemingly chaotic. The number of photons at each rung fluctuates depending on the current powering the laser, which can cause instabilities in the laser’s beam cross-section. These instabilities are often a hindrance to laser applications. However, when photons behave like a Bose-Einstein condensate, most of them accumulate at the lowest energy level, stabilizing the emitted beam. This phenomenon was achieved by designing a laser with an optimal difference between the energy of electron-hole transitions and the energy of the lowest rung of the ladder.’
Where can these new operation principles of semiconductor lasers be applied?
‘That is a great question,’ says Prof. Wasiak. ‘Reports of photonic Bose-Einstein condensates have appeared relatively recently, so for now, the very discovery of their existence is exciting. I am confident that applications will emerge – ones that no one has thought of yet. The fact that we can create such condensates in semiconductor lasers, which are almost identical to the millions of lasers already used in telecommunications, cell phones, and various other devices, will make it much easier to both come up with ideas as well as materialize them.’
Prof. Czyszanowski adds: ‘While the Bose-Einstein condensate will not make lasers more efficient, beyond stabilizing laser emission, it could be of interest if we explore its unique properties, such as photon accumulation at the lowest energy levels. This could function as a kind of logic gate or provide a simulation of quantum systems' behavior on a much larger, more easily observable scale.’
Publication in Nature Materials
The paper Predesigned Perovskite Crystal Waveguides for Room-Temperature Exciton-Polariton Condensation and Edge Lasing, published in Nature Materials, resulted from a collaboration between scientists from Poland, Italy, Iceland, and Australia. Prof. Barbara Piętka, doctoral candidate Mateusz Kędziora, and dr Andrzej Opala of the University of Warsaw played leading roles in the development of this publication.
‘They synthesized layers of perovskites, transforming them into structures analogous to optical integrated circuits. These layers demonstrated the simultaneous potential for both laser action and light propagation, which they confirmed experimentally. They also provided a sophisticated theoretical interpretation of the experimental results,’ explains co-author Prof. Tomasz Czyszanowski, who, using numerical simulations, analyzed the potential for laser action and calculated the waveguide modes observed during the experiments.
According to the physicists, this new technology for producing perovskite crystals holds significant potential for the future of integrated photonics. The researchers have paved the way for groundbreaking applications in photonics by developing innovative methods for fabricating perovskites.