A scientific team has identified the numerical models and analytic estimates for simulating ultra-strong gamma rays in a highly efficient way. According to the team, these high intensity gamma rays significantly exceed all known limits. Gamma rays are electromagnetic waves, just like visible light or x-rays, but with much higher energy. The most energetic gamma rays in the world could be created by the help of advanced laser physics. When the laser light is intense enough and all parameters are right, trapped particles (green) could efficiently convert the laser energy (surfaces in red, orange and yellow) into cascades of super-high energy photons (pink). Courtesy of Arkady Gonoskov. The generation of high-energy photons can induce a cascade of electron-positron pairs that, while creating more photons, rapidly draws too much energy from the system, making the source unsustainable. A team of scientists has discovered a way to overcome such restrictions and create a source of giga-electron-volt (GeV) photons with unprecedented brightness. The team, composed of scientists from Chalmers University of Technology, the Institute of Applied Physics, Lobachevsky University and University of Plymouth, conceived an approach that uses particle-trapping phenomena to initiate a scenario in which particle cascades and highly nonlinear particle dynamics induce and support each other in a controllable manner. By matching the intensity and duration of the laser pulse, the team found that it was possible to induce a cascade that could be held at a subcritical level, avoiding significant depletion effects while sustaining photon production. In this scenario, laser radiation was converted into a well-collimated flash of GeV photons. “The cloud of trapped particles efficiently converts the laser energy into cascades of high energy photons,” said professor Mattias Marklund, who teaches in the physics department at Chalmers. The resulting source had parameters exceeding those provided by existing laser-based sources by several orders of magnitude. Using specially designed advanced numerical models supported with analytical estimates, the team demonstrated that their approach could be feasible at laser powers of around 7 PW, a wavelength that is expected to be accessible at high-intensity laser facilities in the future. Electromagnetic cascades have the potential to act as a high-energy photon source of unprecedented brightness. Such a source would offer new experimental possibilities in fundamental science. “When we exceed the limit of what is currently possible, we can see deeper into the basic elements of nature. We can dive into the deepest part of the atomic nuclei,” said researcher Arkady Gonoskov from Chalmers University. The team believes that its approach is feasible for future large-scale laser facilities and could enable a new era of experiments in photonuclear and quark-nuclear physics. "Our concept is already part of the experimental program proposed for one such facility: Exawatt Center for Extreme Light Studies in Russia. We still don’t know where these studies will lead us, but we know that there are yet things to be discovered within nuclear physics, for example new sources of energy. With fundamental studies, you can aim at something and end up discovering something completely different — which is more interesting and important,” The research was published in Physical Review X (doi: 10.1103/PhysRevX.7.041003).