Small, smaller – microscopically small: An international team of scientists from Germany and Switzerland has succeeded in building the smallest ever nanolaser. It is 300 times thinner than a human hair and works even at room temperature with no need of expensive cooling. The physicists Christopher Gies, Professor Frank Jahnke and Frederik Lohof from the University of Bremen’s Institute for Theoretical Physics (ITP) played an important role in its development with their microscopic models. Thanks to the Bremen experts in laser theory, this is the first time the emission of laser light has been detected on such a miniature scale.
Mini laser for microchips
While laser cutting or scanning CDs is done with a laser that is large enough to be visible to the human eye, applications in information technology, for example, call for much smaller nanolasers. Future data transmission and processing will increasingly be based on light, as we already know from the use of fiber optic cables. For microchips, however, mini-lasers are necessary – the smaller, the more energy-efficient. In addition, they can be integrated directly on the chip, which is an important aspect in addition to energy efficiency. The goal of the international research project was to develop such a nanolaser. The research was funded by the German Research Foundation (DFG) and the Swiss National Science Foundation (SNSF).
Published in “Nature Communications”
The development is an important step for basic research in this path-breaking area. The results, therefore, were also published in the renowned open access journal “Nature Communications” (see link below). The research was realized in close cooperation with other teams headed by leading experts in the field of semiconductor optoelectronics (Prof. Stephan Reitzenstein, TU Berlin), semiconductor processing (Prof. Nicolas Grandjean, École Polytechnique Fédérale de Lausanne), and characterization of nitride semiconductors (Prof. Axel Hoffmann, TU Berlin).
It not only proved extremely difficult to produce the required miniaturized semiconductor structures. Yet another challenge was to prove the existence of phase-coherent light emission – so-called lasing – in the first place. “A normal laser is subject to huge losses,” explains Christopher Gies. “In fact, only 0.0001 percent of the generated light actually ends up in laser mode. The newly developed nanolaser, though, suffers hardly any losses at all – more than 70 percent of the generated light is retained! "
Extremely high energy efficiency
However, the high energy efficiency also presented a problem during the development of the nanolaser. “The almost complete absence of losses means that the laser’s ‘fingerprint’ – namely the sudden increase in light intensity at the laser threshold – is no longer existent. Instead, we have to study the almost unperceivable changes in the small amount of light that is emitted by the tiny semiconductor structure,” explains Gies. “This creates a real problem for experimental measurement methods, because at first you have no idea of which signatures to look for.”
And this is where the expertise of the Bremen University physicists from the Institute for Theoretical Physics came up trumps. Nobody knows better the complex laser theories that take into account the quantum mechanical features of the smallest lasers. With their computer-generated microscopic models, Christopher Gies, Frank Jahnke and Frederik Lohof were able to predict the behavior of the nano-system with amazing accuracy. “When our project partners started on the practical experiments, thanks to our work, they knew exactly how they would be able to identify the presence of lasing. The agreement between theory and experiment was proof that the nano-laser works.
Link zum Nature-Artikel: https://www.nature.com/articles/s41467-018-02999-2; als PDF: https://www.nature.com/articles/s41467-018-02999-2.pdf
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