Compact plasma-based extreme compression of relativistic electron beams

Accelerated particle beams are essential tools of modern science and technology with applications ranging from medicine [1], to light sources [2], to high-energy physics [3]. Over time, as accelerator-based experiments become more sophisticated and probe natural phenomena with greater temporal resolution, there is an increasing demand on beam parameters, in particular on bunch duration. Experiments have been proposed that require beams with 1-2 orders of magnitude shorter durations than what is possible with current state-of-the-art technology. However, state-of-the-art temporal bunch compressors force a trade-off between how short an electron bunch can be made and how well its transverse quality survives the strong bending magnets required to do so -- a limitation that stands as a grand challenge for accelerator physics to-date [4]. In this experiment, we demonstrate a new, compact compression technique for generating ultrashort, high-peak-current electron bunches that circumvents this trade-off using plasma wakefield acceleration. Just as chirped pulse amplification unlocked ultrashort, high-power laser pulses and the technologies that followed from them, here we demonstrate an analogous chirp-and-compress strategy applied to relativistic electron beams by using the extreme electric fields of a plasma wakefield in place of a stretcher-amplifier, thereby unlocking the path to ultrashort, extremely high-current electron beams. We demonstrate the first application of this plasma-compressed bunch using it to drive single-microbunch free electron lasing at optical wavelengths in a single, meter-scale undulator module, producing radiation pulses roughly four orders of magnitude more energetic than the first beam-driven, plasma-based free electron laser demonstration at the same accelerator facility [5, 6].