Abstract-Terahertz-driven linear electron acceleration

Kyung-Han Hong, Ravi Koustuban, Arya Fallahi, Gustavo Moriena, R. J. Miller, Ronny Huang, Franz Kaertner,

http://dspace.mit.edu/handle/1721.1/100509?show=full

The cost, size and availability of electron accelerators are dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency accelerating structures operate with 30–50 MeV m[superscript −1] gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional radio-frequency structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here we demonstrate linear acceleration of electrons with keV energy gain using optically generated terahertz pulses. Terahertz-driven accelerating structures enable high-gradient electron/proton accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. These ultra-compact terahertz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, linear colliders, ultrafast electron diffraction, X-ray science and medical therapy with X-rays and electron beams.

Abstract-Toward a terahertz-driven electron gun

W. Ronny Huang

, Emilio A. Nanni

, Koustuban Ravi

, Kyung-Han Hong

, Arya Fallahi

, Liang Jie Wong

,Phillip D. Keathley

, Luis E. Zapata

 & Franz X. Kärtner

http://www.nature.com/articles/srep14899

Femtosecond electron bunches with keV energies and eV energy spread are needed by condensed matter physicists to resolve state transitions in carbon nanotubes, molecular structures, organic salts, and charge density wave materials. These semirelativistic electron sources are not only of interest for ultrafast electron diffraction, but also for electron energy-loss spectroscopy and as a seed for x-ray FELs. Thus far, the output energy spread (hence pulse duration) of ultrafast electron guns has been limited by the achievable electric field at the surface of the emitter, which is 10 MV/m for DC guns and 200 MV/m for RF guns. A single-cycle THz electron gun provides a unique opportunity to not only achieve GV/m surface electric fields but also with relatively low THz pulse energies, since a single-cycle transform-limited waveform is the most efficient way to achieve intense electric fields. Here, electron bunches of 50 fC from a flat copper photocathode are accelerated from rest to tens of eV by a microjoule THz pulse with peak electric field of 72 MV/m at 1 kHz repetition rate. We show that scaling to the readily-available GV/m THz field regime would translate to monoenergetic electron beams of ~100 keV.

Abstract-A terahertz-driven electron gun

W. Ronny Huang, Emilio A. Nanni, Koustuban Ravi, Kyung-Han Hong, Liang Jie Wong, Phillip D. Keathley, A. Fallahi, Luis Zapata, Franz X. Kärtner

http://arxiv-web3.library.cornell.edu/abs/1409.8668

Electron sources at keV-MeV energies are indispensable for applications such as ultrafast electron diffraction, x-ray generation, and electron energy-loss spectroscopy. However, the accessibility and size of current accelerators based on radio-frequency (RF) technology are limited by the achievable electric fields. Terahertz based accelerators promise unprecedented compactness compared to current RF accelerators due to the intense electric fields that can be applied in the accelerating structures. Here, electron bunches of 50 fC from a flat copper photocathode are accelerated from rest to a mean energy of 18 eV by a single-cycle THz field with peak electric field gradient of 72 MV/m at 1 kHz repetition rate. Scaling of the THz field into the gigavolt per meter regime would translate to electron energies of ~100 keV. Furthermore, in combination with the recent demonstration of a THz linear accelerator (linac), this is a milestone toward a millimeter- to centimeter-scale relativistic electron source.