Generating ultra-bright radiation with faster-than-light “particles”
An international team of physicists led by scientists from IPFN’s Group of Lasers and Plasmas (GoLP) discovered that slow particles may hold the key to a new class of light sources, as powerful as the most advanced today, but at a fraction of the size.
Their work has just been published in Nature Photonics, one of the scientific journals with the greatest impact in the field. The team also includes researchers and academics from the University of Rochester, the University of California (both in the United States) and the Applied Optics Laboratory in France.
“Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws”. The words of British writer and humourist Douglas Adams contradict one of the pillars of Albert Einstein's theory of relativity, according to which nothing can travel faster than light. But what would happen if there were particles that actually could?
To get around this limit, the researchers used a trick: instead of individual particles that, in fact, cannot travel faster than light, they thought of using the so-called 'quasi-particles' which, in this case, result from the synchronized motion of electrons.
It turns out that quasi-particles can travel at any speed, even above the speed of light. For John Palastro, co-author of this study and professor at the University of Rochester, “The most fascinating aspect of quasiparticles is their ability to move in ways that would be disallowed by the laws of physics governing individual particles,”, simply by being able to reorganize the motion of electrons appropriately. This flexibility opens up a set of completely unknown and unexplored possibilities.
According to Jorge Vieira, professor at Instituto Superior Técnico and mentor of the study, “these radiant quasi-particles give us the possibility of building super light sources that work from a completely new principle. It’s a very refreshing idea.” He argues that the simplicity of the approach makes it suitable for experiments in dozens or even hundreds of laboratories around the world, bringing the theoretical concept closer to reality and the near future.
Bernardo Malaca, PhD student at Técnico and first author of the study, explains: “We start from the fundamentals – what are the conditions for several particles to radiate as one? – and then we applied that to the most intense light sources.”
Light sources have a profound social impact on science and technology. Some illustrative examples are non-destructive imaging (such as used in airport security to check baggage), biology (understanding of processes such as photosynthesis), technological applications (manufacturing chips for electronic circuits) and physical sciences (understanding the behaviour of matter inside planets and stars).
Free electron lasers (FEL), the brightest radiation sources so far, are rare – there are not many more than 10 countries around the world with these devices, with Portugal not among them. In addition to their size (up to several km long), the cost and complexity of FELs make them unfeasible for use in laboratories at universities, hospitals and companies.
According to this new theory, quasi-particles must only travel a few tenths of a millimetre to produce extremely bright light. As such, these sources could cause a small scientific and social revolution, if they are demonstrated in the laboratory.
To know more:
Malaca, B., Pardal, M., Ramsey, D. et al. Coherence and superradiance from a plasma-based quasiparticle accelerator. Nat. Photon. (2023).
Ultra-bright light breakthrough could spark 'technological and scientific revolution' (BBC science focus)
Faster-than-light 'quasiparticles' touted as futuristic light source(Gizmodo)
