A New Scheme for Recording Electron Bunch Shapes With High Resolution and Record Recording Length - Principle and Tests at EuXFEL

Recording electron bunch longitudinal profiles in single-shot, and non-destructively is largely needed in accelerator operation. A common strategy consists in probing the near-field of the bunch using femtosecond laser pulses. These two last decades, such electro-optic detection schemes have evolved to compact and reliable techniques. However, serious limitations have been limiting the time-resolution, when long recording lengths are needed. This has been recognized as a fundamental bottleneck and even coined the term "Fourier limit". We present here a novel electro-optic sampling strategy that is theoretically capable to overcome this limit and achieve femtosecond resolution for any recording length. This new approach is based on the mathematical concept of information diversity. We present first results of DEOS (Diversity Electro-Optic Sampling) obtained both in table-top experiments, as well as at the European XFEL. This technique opens the way to electric field shape characterization with femtosecond resolution in new situations, including longitudinal bunch profile monitoring, studies of microbunching instabilities, and THz pulses generated at free-electron lasers