The enormous size and cost of current state-of-the-art accelerators based on conventional radio-frequency technology has spawned great interest in the development of new acceleration concepts that are more compact and economical. Micro-fabricated dielectric laser accelerators (DLAs) are an attractive approach, because such dielectric microstructures can support accelerating fields one to two orders of magnitude higher than can radio-frequency cavity-based accelerators. DLAs use commercial lasers as a power source, which are smaller and less expensive than the radio-frequency klystrons that power today’s accelerators. In addition, DLAs are fabricated via low-cost, lithographic techniques that can be used for mass production. However, despite several DLA structures having been proposed recently1,2,3,4, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250 MeV m−1) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563 ± 104 optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of 10–30 MeV m−1, and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6 MeV m−1 (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the MeV–GeV (106–109 eV) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV (1012 eV) scale.
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We thank R. Noble, J. Spencer, O. Solgaard and J. Harris for discussions, J. Nelson, D. McCormick and K. Jobe for technical assistance at SLAC, and M. Tang, M. Mansourpour, N. Latta, M. Stevens, J. Conway and U. Thumser for technical assistance at the Stanford Nanofabrication Facility (SNF). This work was supported by the US DoE (grant no. DE-FG03-92ER40693) and DARPA (grant no. N66001-11-1-4199). Device fabrication took place at SNF, which is supported by the NSF under grant ECS-9731293. Work by G.T., J.M. and E.B.S. supported by US Defense Threat Reduction Agency (DTRA) grant HDTRA1-09-1-0043.
The authors declare no competing financial interests.
Extended data figures and tables
a, Diagram of the structure fabrication process. In side view, the electron beam traverses the structure from left to right. In front view, the beam goes into the page. Laser is incident from above. See Methods for details. b, Picture of a completed wafer with hundreds of DLA structures. c, Diagram of a finished sample ready for beam tests including four DLA structures, alignment channels, a wedge for spatial alignment of the laser to the electron beam, and a metal coating for perpendicular alignment of the laser. d, Picture of a single DLA structure on a fingertip.
a, Spectrometer screen image showing the 60-MeV beam with no DLA structure in place. b, Spectrometer screen image of the beam after traversing the grating structure. c, Projection of b onto the energy axis yields the energy spectrum (black crosses) in agreement with particle scattering simulations (blue dots). The corresponding least squares spectrum fit (orange curve) is also shown.
a, Picosecond-scale electron beam partitioned into a series of finite slices over one optical cycle of the laser (for example, the green slice is at optimal phase for acceleration). b, Each slice samples a different phase of the laser pulse and therefore experiences a corresponding net energy shift with a negligible effect on the energy profile (for example, the green slice experiences net energy gain). c, When all contributions are superimposed, the initial single distribution (dashed blue line) becomes a double-peaked profile (red line), in agreement with particle tracking simulations (black crosses).
Calculated gradient (blue filled circles) G as a function of longitudinal electric field E0 showing expected linear dependence (dashed blue line) and reduced strength when compared to the 400-nm gap structure, as expected for a larger gap. The dashed black line is the measurement noise level. Error bars, 68% confidence interval.
a, Gradient in the 800-nm gap structure for an input pulse energy of 105.2 ± 3.6 µJ. As the laser polarization is rotated away from the direction of electron propagation by an angle ϕ, the acceleration gradient varies as G ∝ cosϕ. Data for ϕ < 0 were taken last, and beam quality had degraded. b, Gradient in the 400-nm gap structure at an input pulse energy of 29.3 ± 0.4 µJ, averaging the observed modulation over many shots taken at an optimal timing overlap. As the laser incidence angle deviates from perpendicular by an angle θ, the observed gradient decreases according to the expected relationship, equation (2) in Supplementary Information. Data are shown as blue filled circles with the corresponding least squares fit shown as green lines. The dashed black line is the measurement noise level. Error bars, 68% confidence interval.
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Peralta, E., Soong, K., England, R. et al. Demonstration of electron acceleration in a laser-driven dielectric microstructure. Nature 503, 91–94 (2013). https://doi.org/10.1038/nature12664
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