All-optical free-electron lasers with Traveling-wave Thomson-scattering -- Theory and scaling

In Traveling-Wave Thomson-Scattering (TWTS) an optical, high-power laser pulse is scattered off a relativistic electron pulse to realize optical ree-electron lasers (OFELs) with a wavelength ranging from ultraviolet to Angstrom [*].

Such TWTS-OFELs optimally exploit the high spectral photon density in high-power laser pulses by spatially stretching the laser pulse and overlapping it with the electrons in a side scattering setup. The introduction of a laser pulse-front tilt provides for interaction lengths appropriate for FEL operation, so that beam electrons witness an undulator field of near-constant strength and wavelength over hundreds to thousands of undulator periods, thus giving enough time for self-amplified spontaneous emission (SASE) to seed the FEL instability and the realization of large laser gains.

In contrast to head-on OFEL schemes, TWTS-OFEL operates at sub-mm to mm effective undulator wavelength. Thus previous show-stoppers to OFELs due to small transverse coherence, large space charge or significant quantum effects are avoided. One of the key advantages of this approach is its scalability to x-ray wavelengths with existing lasers. We present the complete analytical description of the TWTS field and a self-consistent 1.5D theory of TWTS OFELs. We discuss the main scalings of resulting
TWTS OFELs with respect to electron and laser beam properties.