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Scientists in Germany are attempting to build the world’s smallest particle accelerator – and it is going to be so small that it fits on a microchip.
Professor Doctor Peter Hommelhoff and his research group at the Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) have moved a step closer towards achieving this ambition by developing a new technique concerning the meeting of two laser beams fluctuating at different frequencies to generate an optical field with properties that can be influenced incredibly precisely.
The central idea behind developing a miniature particle accelerator is to allow Scientists to use laser beams to accelerate electrons. It will work in a similar way to the Large Hadron Collider (LHC) – perhaps the most well-known and largest particle accelerator – just on a much smaller scale.
It sounds deceivingly simple in theory, but in practice it raises a whole series of challenges extending across various fields of physics. For example, the Scientists need to be able to control the oscillation of light and the movement of electrons with great precision to ensure they collide at just the right moment.
The team have to ascertain when and where the maximum crest of a light wave will hit a packet of electrons so that they can influence the outcome to a highly specific degree. This means the Researchers need to ensure the light and the electrons collide within attoseconds – that is, within a billionth of a billionth of a second.
In an exciting first, this is exactly what Professor Hommelhoff and his team in the Department of Condensed Matter Physics have managed to achieve. They developed a new technique involving the intersection of two laser beams oscillating at different frequencies in order to generate an optical field whose properties the Researchers can influence to an extremely precise degree.
One of the key properties of this optical field is that it remains in contact with the electrons, moving along with them – hence being called a traveling wave – so the electrons continuously sense or surf the optical fields. This means the optical field transmits its properties precisely to the particles.
This process causes the particles to exactly reflect the field structure while also being accelerated to an incredibly high degree. This effect is crucial to the practical application of the miniature particle accelerator as it is related to how much energy can be transferred to the electrons across what distance.
The acceleration gradient - which indicates the maximum measured electron energy gain versus the distance covered - reaches a massive 2.2 giga-electron-volts per meter, much higher than that attained by conventional accelerators. However, the acceleration distance of only 0.01 millimeters currently available is not enough for the FAU research team to generate the energy needed for achieving results of relevance to practical applications.
Despite this, for particle accelerators in medicine, we would only need a tiny acceleration length of less than a millimeter.
Dr Martin Kozák, Chair of Laser Physics, the Department of Condensed Matter Physics
Professor Hommelhoff, who is the Project Leader and Chair of Laser Physics at FAU, believes accelerator miniaturization to be a technical revolution analogous to the development of computers, which once filled entire rooms and now fit on people's wrists.
This approach will hopefully enable us to make this innovative particle acceleration technique usable in a range of research areas and fields of application such as materials science, biology and medicine; one example might be particle therapies for cancer patients.
Professor Hommelhoff, Project Leader and Chair of Laser Physics, FAU
The team have published their work online in Nature Physics.