Towards single-cycle attosecond light from accelerators

The Free-Electron Laser (FEL) is a cutting-edge, accelerator-based instrument that has the potential to provide simultaneous access to the spatial and temporal resolution of the atomic world. In a FEL, ultra-short electron bunches from an accelerator are passed through a long undulator magnet to generate coherent light. Recently, scientists from SLAC demonstrated the first generation of attosecond hard X-ray pulses, using the Linac Coherent Light Source. Now, as described in the review article by Alan Mak et al. [1], researchers are proposing developments that will make the FEL a fully coherent, singlecycle (attosecond) X-ray laser. The new concepts build upon a strong nexus between linear accelerators, FELs and quantum lasers, to produce extreme attosecond pulses with controllable waveforms.