Fundamental physics with an X-ray free electron laser

Of late, laboratories around the world are considering building X-ray free electron lasers based on high energy electron accelerators (with energies exceeding 10 GeV) to produce bright coherent X rays with wavelengths on the order of 1 Å. Because of the extremely small wavelength and high brilliance of these coherent X rays, there is an unprecedented opportunity to explore new applications of what is sometimes called the fourth generation of light sources. Here, we point out that in addition to the anticipated applications to material science and biology, a number of applications to fundamental physics may become possible in the fields of extreme high-energy accelerating gradients, ultrahot matter creation, coherent γ-ray generation, violent acceleration and “horizon physics,” and nonlinear field theory (quantum electrodynamics). Intensive development in technical areas, particularly that of X-ray optics, will be needed, however, in order to achieve ultrahigh intensity X-rays that can allow these applications.