Are light and charged particle beams two sides of a same coin?

When particle acceleration was observed for the first time in history, scientists named the electron beams “cathode rays”. One could say retrospectively that this was one of the first insights into the unification of the behaviour of matter and of light. In the 20th century, in fact, quantum mechanics torn apart the boundary between (anti)matter and light, which is ultimately energy. We now are not shocked anymore when we are told that everything has a double nature, behaving both as wave and as corpuscular particle. Beforehand, these two kinds of behaviours were respectively associated to two different phenomena.

KEK Linear Accelerator mounting electromagnetic lenses (quadrupoles). Credit:  yellow_bird_woodstock (WikiMedia Commons).

KEK Linear Accelerator mounting electromagnetic lenses (quadrupoles). Credit: yellow_bird_woodstock (WikiMedia Commons).

This dualism is not limited to physics but appeared also in the realm of technology. In fact, it is possible to spot several analogies among particle accelerators and light science and technology. For instance, to design an accelerator, physicists and engineers talk about “optics” and “lattice”. These terms are also used for laser technologies: the “colour” of the beams of light emitted depends on the crystalline structure, that is the lattice in which atoms are organised; when studying the propagation of the beam of photons, material lenses form the optics, to focus and control the beam.

Particle accelerators act based on mirror concepts: beams of (anti)matter particles are kept stable by a special arrangement (lattice) of magnetic and electric fields – which are a non-visible kind of light; moreover they are focused and controlled thanks to “optics” elements, that manipulate the beam through electromagnetic fields. Chromaticity, which is the dependence of the focal length of a lens on the frequency of the light, exists exactly in the same way for material lenses focusing light and electromagnetic lenses focusing charged particle beams.

This is concerning the technology of the present, but there are several common points also in the development of future technologies. Novel accelerator technologies use lasers to extract particles from targets and to accelerate them, but also accelerators themselves are used to spark light emission at frequencies yet unachievable by solid state matter thanks to the synchrotron radiation emitted by charged particle beams traveling along curved paths in synchrotrons. Moreover, detectors in colliders use the light produced from the particles collisions are a key ingredient to detect particles decay and interactions, thus being fundamental to lead to new discoveries.

The connection between the two phenomena is so strong that scientists are investigating the “inverse” phenomena of radiation-matter interaction to give birth to some of present and future technologies: the inverse-compton scattering could lead to a new generation of light sources, the inverse-smith purcell effect is investigated to develop new accelerating nanofabricated structures, the recent observation of pair-production from photon-photon collision has lead to the concept of a photon-photon collider. The latter would be a machine made of laser beams colliding with each other to produce charged particles, thus showing the full exploitability of the symmetry between charged particles and light beams.

The exploration has just begun, and the further we go the more light and accelerators science and technologies become challenging and fascinating.


Summary of the characteristics of the symmetric phenomena described in the article


author pictureGiovanna Campogiani (@alea88) is an Electronics Engineer from Sapienza University of Rome, pursuing a PhD in Accelerator Physics. She is currently working at the European Centre for Nuclear Research (CERN) to develop a model for collider luminosity. Her research interests include also novel accelerator technologies and light sources.

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