Laser Optics Particle Accelerator Concept
Science & Technology

The Paradox of a Free-Electron Laser Without the Laser: A New Source of Coherent Radiation

Laser Optics Particle Accelerator Concept

A new method of producing coherent mild in the ultra-violet spectral area, which factors the option to creating good table-top x-ray sources, has been produced in analysis led at the College of Strathclyde.

The scientists have developed a kind of ultra-short wavelength coherent mild supply that doesn’t require laser motion to provide coherence. Frequent electron-beam based mostly mild sources, often called fourth-generation mild sources, are based mostly on the free-electron laser (FEL), which makes use of an undulator to transform electron beam power into X-rays.

Coherent mild sources are highly effective instruments that allow analysis in lots of areas of drugs, biology, materials sciences, chemistry, and physics.

“This new method of producing coherent radiation might revolutionise mild sources, as it might make them extremely compact, basically table-top measurement, and succesful of producing ultra-short period pulses of mild, a lot shorter than could be produced simply by some other means.”

Making ultraviolet and X-ray coherent mild sources extra broadly obtainable would remodel the method science is completed; a college might have one of the units in a single room, on a desk prime, for a affordable value.

The group is now planning a proof-of-principle experiment in the ultraviolet spectral vary to exhibit this new method of producing coherent mild. If profitable, it ought to dramatically speed up the improvement of even shorter wavelength coherent sources based mostly on the identical precept. The Strathclyde group has arrange a facility to analyze these sorts of sources: the Scottish Centre for the Utility of Plasma-based Accelerators (SCAPA), which hosts one of the highest energy lasers in the UK.

The new analysis has been printed in Scientific Studies, one of the Nature household of journals.

Professor Dino Jaroszynski, of Strathclyde’s Division of Physics, led the analysis. He stated: “This work considerably advances the state-of-the-art of synchrotron sources by proposing a new technique of producing short-wavelength coherent radiation, utilizing a brief undulator and attosecond period electron bunches.

“That is extra compact and fewer demanding on the electron beam high quality than free-electron lasers and will present a paradigm shift in mild sources, which might stimulate a new path of analysis. It proposes to make use of bunch compression – as in chirped pulse amplification lasers – inside the undulator to considerably improve the radiation brightness.

“The new technique introduced can be of broad curiosity to a various neighborhood creating and utilizing mild sources.”

In FELs, as in all lasers, the depth of mild is amplified by a suggestions mechanism that locks the phases of particular person radiators, which on this case are “free” electrons. In the FEL, that is achieved by passing a excessive power electron beam by way of the undulator, which is an array of alternating polarity magnets.

Mild emitted from the electrons as they wiggle by way of the undulator creates a drive referred to as the ponderomotive drive that bunches the electrons – some are slowed down, some are sped up, which causes bunching, just like visitors on a motorway periodically slowing and dashing up.

Electrons passing by way of the undulator radiate incoherent mild if they’re uniformly distributed – for each electron that emits mild, there may be one other electron that partially cancels out the mild as a result of they radiate out of part. An analogy of this partial canceling out is rain on the sea: it produces many small ripples that partially cancel one another out, successfully quelling the waves – lowering their amplitude. In distinction, regular or pulsating wind will trigger the waves to amplify by way of the mutual interplay of the wind with the sea.

In the FEL, electron bunching causes amplification of the mild and the improve in its coherence, which normally takes a very long time – thus very lengthy undulators are required. In an X-ray FEL, the undulators could be greater than a hundred meters lengthy. The accelerators driving these X-ray FELs are kilometers lengthy, which makes these units very costly and a few of the largest devices in the world.

Nonetheless, utilizing a free-electron laser to provide coherent radiation shouldn’t be the solely method; a “pre-bunched” beam or ultra-short electron bunch may also be used to realize precisely the identical coherence in a very brief undulator that’s lower than a meter in size. So long as the electron bunch is shorter than the wavelength of the mild produced by the undulator, it should routinely produce coherent mild – all the mild waves will add up or intervene constructively, which ends up in very good mild with precisely the identical properties of mild from a laser.

The researchers have demonstrated theoretically that this may be achieved utilizing a laser-plasma wakefield accelerator, which produces electron bunches that may have a size of a few tens of nanometers. They present that if these ultra-short bunches of excessive power electrons cross by way of a brief undulator, they’ll produce as might photons as a very costly FEL can produce. Furthermore, they’ve additionally proven that by producing an electron bunch that has an power “chirp,” they’ll ballistically compress the bunch to a very brief period inside the undulator, which offers a distinctive method of going to even shorter electron bunches and subsequently produce even shorter wavelength mild.

Reference: “Vacuum ultraviolet coherent undulator radiation from attosecond electron bunches” by Enrico Brunetti, Bas van der Geer, Marieke de Loos, Kay A. Dewhurst, Andrzej Kornaszewski, Antoine Maitrallain, Bruno D. Muratori, Hywel L. Owen, S. Mark Wiggins and Dino A. Jaroszynski, 16 July 2021, Scientific Studies.
DOI: 10.1038/s41598-021-93640-8

The analysis collaboration additionally concerned the College of Manchester, Pulsar Physics in the Netherlands and the STFC ASTeC group at Daresbury Laboratories. The examine has acquired funding from the EPSRC (Engineering and Bodily Sciences Analysis Council), to help a undertaking named Lab in a Bubble.

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