Nature Commun. 6, 8486 (2015)

Optical schemes for charged particle acceleration are highly desirable. Usually such schemes, the most popular being the laser-driven wakefield accelerator, rely on intense femtosecond laser sources with demanding properties. Now, an international collaboration of scientists from the US, Canada and Germany have demonstrated that the use terahertz (THz) pulses could perhaps ease requirements with the report of a THz-driven linear accelerator for electrons. The team report how an optically generated 10 μJ THz pulse centred at 0.45 THz was able to accelerate electrons along a 3-mm-long circular-profile dielectric waveguide with a copper outer wall. In this proof-of-principle experiment the energy of the accelerated electrons is boosted by 7 keV, but it is expected that the use of more intense THz sources would be able to provide GeV m−1 acceleration gradients. The development of ultracompact THz accelerators that support extremely short electron bunches would potentially prove valuable for free-electron lasers, linear colliders and X-ray science. The single-cycle THz pulses used in the experiments were generated by optical rectification of 1.2 mJ, 1.03 μm laser pulses with a repetition rate of 1 kHz. A segmented waveplate was used to transform the polarization of the THz pulses from a linear to a radial polarization, prior to them being coupled into the waveguide, to accelerate 60 keV electrons emitted from an electron gun.