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The Center for Bright Beams, A National Science Foundation Science and Technology Center

New Discoveries May Have Real-World Impact on DLA, XFEL, and UED Applications

Research Theme

Beam Production
Published April 8, 2024

High peak current electron beams are of fundamental importance in next generation linear accelerator-based facilities such as ultrafast and ultrasmall tools like Dielectric Laser Accelerator (DLA), X-Ray Free Electron Lasers (XFELs), particle colliders, Ultrafast Electron Diffraction (UED) and inverse Compton scattering experiments. Other applications include terahertz devices, nano-electronics, and various biomedical imaging applications.

Nitrogen incorporated Ultrananocrystalline Diamond, (N)UNCD, along with other carbon-based sources, have been of great interest in recent years for high peak current applications owing to its high electrical conductivity and vacuum robustness. In this work, we report study of ultrafast non-linear photoemission mechanisms from nanostructured (N)UNCD pyramid tip cathode. We report the measurements of the scaling of the electron count rate with the incident laser intensity and the first ever measurement of photoemission electron kinetic energy spectra (PEES) from (N)UNCD pyramid tip cathode using photoemission electron microscope (PEEM). We observe the change in non-linearity in the electron count rate with increasing incident laser intensity.  The PEES spectra show electrons with kinetic energies as high as ~10 eV. Based on the shape of the PEES spectra we conclude that the high energy electrons are thermally emitted electrons due to ultrafast laser heating at the tip of (N)UNCD pyramid tip cathode.

The authors believe that this work presents scientific advances that lie at the juncture of photocathode physics, accelerator physics and solid-statephysics, and takes critical steps towards advancing real world applications like DLA, XFEL and UED. Moreover, these results will have a direct impact on the choice of the photocathode and the electron gun design of several novel ultrafast and ultrasmall future particle accelerator facilities.

(a) Structural change in the tip at the apex of (N)UNCD PTC after irradiation with femtosecond laser with the pulse length of 150 fs and central wavelength of 800 nm (b) (N)UNCD PTC showing laser-induced periodic surface structures (LIPSS) on the pyramid face exposed to the incident laser. The LIPSS were oriented perpendicular to the direction of the electric field of the incident laser with a spatial period of the order of 800 nm.
(a) Structural change in the tip at the apex of (N)UNCD PTC after irradiation with femtosecond laser with the pulse length of 150 fs and central wavelength of 800 nm (b) (N)UNCD PTC showing laser-induced periodic surface structures (LIPSS) on the pyramid face exposed to the incident laser. The LIPSS were oriented perpendicular to the direction of the electric field of the incident laser with a spatial period of the order of 800 nm.

Related References

[1] Kachwala, A., Chubenko, O., Kim, D., Simakov, E.I. and Karkare, S., 2024. Ultrafast laser triggered electron emission from ultrananocrystalline diamond pyramid tip cathode. Journal of Applied Physics, 135(12).

[2] Kachwala, A., Chubenko, O., Kim, D., Simakov, E.I. and Karkare, S., 2022. Quantum efficiency, photoemission energy spectra, and mean transverse energy of ultrananocrystalline diamond photocathode. Journal of Applied Physics, 132(22).

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