Particle accelerators found numerous applications in industrial processes, medicine and fundamental research. In industry, accelerated particles are used for etching and for local modification of material properties, while in medicine they are applied for radiation therapy, and physicists use accelerators for studying the fundamental structure of matter. There are a great variety of accelerators, but they all use the same principle – to accelerate charged particles one needs to apply an electric field along the particle trajectory. The energy acquired by a particle depends on its charge, the electric field strength and the distance it travels. The charge is fixed by the type of particle you want to accelerate, and the achievable electric fields are usually limited; this is why a lot of accelerators are rather big. At the same time, the availability of efficient lasers producing electromagnetic waves with tremendous energy fluxes and electric field intensities stimulates the study of the possibility of new types of particle accelerators. In the past several years there has been an increase in the number of publications suggesting the miniaturization of particle accelerators by using the large electric fields produced by lasers.
In this work, the authors have taken the challenge of producing the key building block for an extremely compact particle accelerator. This accelerator was theoretically suggested earlier, and its operation is based on particle acceleration by the longitudinal mode of a photonic crystal waveguide. While the idea is excellent, the manufacturing of a three-dimensional photonic crystal of complex shape still remains a serious problem. I. Staude and co-authors used their extensive experience in nanostructure fabrication in order to create the required photonic crystal waveguides. Just to highlight the complexity of the process used in this work, we mention that the authors first applied direct laser writing to create polymer templates, and then they used silicon double inversion in order to make the required structure out of silicon. They demonstrated that their structure supports the electromagnetic mode required for accelerating particles, giving us hope that on-chip particle accelerators can be realized in the near future.
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