Traveling-wave Thomson Scattering towards tunable, high-yield sources in the hard X-ray range

Thomson sources are compact in size and can provide ultrashort, hard X-ray pulses of high brilliance. However, the finite Rayleigh length at small interaction diameters, makes it increasingly difficult in head-on (180°) Thomson scenarios to avoid higher laser intensities and thus the onset of the nonlinear regime. Effectively, such a geometry limits the peak brilliance of all future Thomson sources. We present a novel concept, Traveling-wave Thomson scattering (TWTS), which allows to obtain centimeter to meter long optical undulators, where interaction length and diameter are independent of each other. With an ultrashort, high-power laser pulse in an oblique angle scattering geometry using tilted pulse fronts, electrons and laser remain overlapped while both beams travel over distances much longer than the Rayleigh length. TWTS offers per pulse photon yields that are 2-3 orders of magnitudes beyond current designs, a minimum scattered bandwidth independent of the ultrashort laser pulse duration and tunability of photon energy without requiring a change in electron energy.