Towards graphene plasmon-based free-electron infrared to X-ray sources


Rapid progress in nanofabrication methods has fuelled a quest for ultra-compact photonic integrated systems and nanoscale light sources. The prospect of small-footprint, high-quality emitters of short-wavelength radiation is especially exciting due to the importance of extreme-ultraviolet and X-ray radiation as research and diagnostic tools in medicine, engineering and the natural sciences. Here, we propose a highly directional, tunable and monochromatic radiation source based on electrons interacting with graphene plasmons. Our complementary analytical theory and ab initio simulations demonstrate that the high momentum of the strongly confined graphene plasmons enables the generation of high-frequency radiation from relatively low-energy electrons, bypassing the need for lengthy electron acceleration stages or extreme laser intensities. For instance, highly directional 20 keV photons could be generated in a table-top design using electrons from conventional radiofrequency electron guns. The conductive nature and high damage threshold of graphene make it especially suitable for this application. Our electron–plasmon scattering theory is readily extended to other systems in which free electrons interact with surface waves.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: GP-based free-electron source of short-wavelength radiation.
Figure 2: Numerical versus analytical results of the radiation spectrum.
Figure 3: Regimes of frequency conversion for the GP-based free-electron radiation source.


  1. 1

    Jablan, M., Soljacic, M. & Buljan, H. Plasmons in graphene: fundamental properties and potential applications. Proc. IEEE 101, 1689–1704 (2013).

    Article  Google Scholar 

  2. 2

    Koppens, F. H. L., Chang, D. E. & de Abajo, F. J. G. Graphene plasmonics: a platform for strong light–matter interactions. Nano Lett. 11, 3370–3377 (2011).

    ADS  Article  Google Scholar 

  3. 3

    Woessner, A. et al. Highly confined low-loss plasmons in graphene–boron nitride heterostructures. Nature Mater. 14, 421–425 (2015).

    ADS  Article  Google Scholar 

  4. 4

    De Abajo, F. J. G. Graphene plasmonics: challenges and opportunities. ACS Photon. 1, 135–152 (2014).

    Article  Google Scholar 

  5. 5

    Fei, Z. et al. Gate-tuning of graphene plasmons revealed by infrared nano-imaging. Nature 487, 82–85 (2012).

    ADS  Article  Google Scholar 

  6. 6

    Chen, J. et al. Optical nano-imaging of gate-tunable graphene plasmons. Nature 487, 77–81 (2012).

    ADS  Article  Google Scholar 

  7. 7

    Alonso-González, P. et al. Controlling graphene plasmons with resonant metal antennas and spatial conductivity patterns. Science 344, 1369–1373 (2014).

    ADS  Article  Google Scholar 

  8. 8

    Yao, Y. et al. Broad electrical tuning of graphene-loaded plasmonic antennas. Nano Lett. 13, 1257–1264 (2013).

    ADS  Article  Google Scholar 

  9. 9

    Fang, Z. et al. Plasmon-induced doping of graphene. ACS Nano 6, 10222–10228 (2012).

    Article  Google Scholar 

  10. 10

    Yan, H. et al. Damping pathways of mid-infrared plasmons in graphene nanostructures. Nature Photon. 7, 394–399 (2013).

    ADS  Article  Google Scholar 

  11. 11

    Ju, L. et al. Graphene plasmonics for tunable terahertz metamaterials. Nature Nanotech. 6, 630–634 (2011).

    ADS  Article  Google Scholar 

  12. 12

    Grigorenko, A. N., Polini, M. & Novoselov, K. S. Graphene plasmonics. Nature Photon. 6, 749–758 0.1038/nphoton.2015.256(2012).

    ADS  Article  Google Scholar 

  13. 13

    Low, T. & Avouris, P. Graphene plasmonics for terahertz to mid-infrared applications. ACS Nano 8, 1086–1101 (2014).

    Article  Google Scholar 

  14. 14

    Lukianova-Hleb, E. Y. et al. On-demand intracellular amplification of chemoradiation with cancer-specific plasmonic nanobubbles. Nature Med. 20, 778–784 (2014).

    Article  Google Scholar 

  15. 15

    Bargheer, M., Zhavoronkov, N., Woerner, M. & Elsaesser, T. Recent progress in ultrafast X-ray diffraction. ChemPhysChem. 7, 783–792 (2006).

    Article  Google Scholar 

  16. 16

    Rousse, A. et al. Femtosecond X-ray crystallography. Rev. Mod. Phys. 73, 17–31 (2001).

    ADS  Article  Google Scholar 

  17. 17

    Bressler, C. & Chergui, M. Ultrafast X-ray absorption spectroscopy. Chem. Rev. 104, 1781–1812 (2004).

    Article  Google Scholar 

  18. 18

    Adamo, G. et al. Light well: a tunable free-electron light source on a chip. Phys. Rev. Lett. 104, 024801 (2010).

    Article  Google Scholar 

  19. 19

    Smith, S. J. & Purcell, E. M. Visible light from localized surface charges moving across a grating. Phys. Rev. 92, 1069 (1953).

    ADS  Article  Google Scholar 

  20. 20

    Friedman, A., Gover, A., Kurizki, G., Ruschin, S. & Yariv, A. Spontaneous and stimulated emission from quasifree electrons. Rev. Mod. Phys. 60, 471–535 (1988).

    ADS  Article  Google Scholar 

  21. 21

    Gover, A., Dvorkis, P. & Elisha, U. Angular radiation pattern of Smith–Purcell radiation. J. Opt. Soc. Am. B 1, 723–728 (1984).

    ADS  Article  Google Scholar 

  22. 22

    Karagodsky, V., Schieber, D. & Schächter, L. Enhancing X-ray generation by electron-beam–laser interaction in an optical Bragg structure. Phys. Rev. Lett. 104, 024801 (2010).

    ADS  Article  Google Scholar 

  23. 23

    Geim, A. K. Graphene: status and prospects. Science 324, 1530–1534 (2009).

    ADS  Article  Google Scholar 

  24. 24

    Zhou, W. et al. Atomically localized plasmon enhancement in monolayer graphene. Nature Nanotech. 7, 161–165 (2012).

    ADS  Article  Google Scholar 

  25. 25

    Brar, V. W., Jang, M. S., Sherrott, M., Lopez, J. J. & Atwater, H. A. Highly confined tunable mid-infrared plasmonics in graphene nanoresonators. Nano Lett. 13, 2541–2547 (2013).

    ADS  Article  Google Scholar 

  26. 26

    Jablan, M., Buljan, H. & Soljacic, M. Plasmonics in graphene at infrared frequencies. Phys. Rev. B 80, 245435 (2009).

    ADS  Article  Google Scholar 

  27. 27

    Hwang, E. H. & Das Sarma, S. Dielectric function, screening, and plasmons in two-dimensional graphene. Phys. Rev. B 75, 205418 (2007).

    ADS  Article  Google Scholar 

  28. 28

    Wunsch, B., Sauber, T., Sols, F. & Guinea, F. ‘Dynamic polarization of graphene at finite doping. New J. Phys. 8, 318 (2006).

    ADS  Article  Google Scholar 

  29. 29

    Page, A. F., Ballout, F., Hess, O. & Hamm, J. M. Nonequilibrium plasmons with gain in graphene. Phys. Rev. B 91, 075404 (2015).

    ADS  Article  Google Scholar 

  30. 30

    Liu, G. et al. Epitaxial graphene nanoribbon array fabrication using BCP-assisted nanolithography. ACS Nano 6, 6786–6792 (2012).

    Article  Google Scholar 

  31. 31

    Brar, V. W. et al. Observation of carrier-density-dependent many-body effects in graphene via tunneling spectroscopy. Phys. Rev. Lett. 104, 036805 (2010).

    ADS  Article  Google Scholar 

  32. 32

    Zhang, Q. et al. Graphene surface plasmons at the near-infrared optical regime. Sci. Rep. 4, 6559 (2014).

    Article  Google Scholar 

  33. 33

    Tielrooij, K. J. et al. Electrical control of optical emitter relaxation pathways enabled by graphene. Nature Phys. 11, 281–287 (2015).

    ADS  Article  Google Scholar 

  34. 34

    Jackson, J. D. Classical Electrodynamics 2nd edn (Wiley, 1975).

    Google Scholar 

  35. 35

    England, R. J. et al. Dielectric laser accelerators. Rev. Mod. Phys. 86, 1337 (2014).

    ADS  Article  Google Scholar 

  36. 36

    Roberts, A. et al. Response of graphene to femtosecond high-intensity laser irradiation. Appl. Phys. Lett. 99, 051912 (2011).

    ADS  Article  Google Scholar 

  37. 37

    Graves, W. S., Kärtner, F. X., Moncton, D. E. & Piot, P. Intense superradiant X rays from a compact source using a nanocathode array and emittance exchange. Phys. Rev. Lett. 108, 263904 (2012).

    ADS  Article  Google Scholar 

  38. 38

    Nanni, E. A., Graves, W. S. & Moncton, D. E. Nano-modulated electron beams via electron diffraction and emittance exchange for coherent X-ray generation. Preprint at http://arXiv:1506.07053 [physics.acc-ph].

  39. 39

    Stauber, T. & Gómez-Santos, G. Plasmons and near-field amplification in double-layer graphene. Phys. Rev. B 85, 075410 (2012).

    ADS  Article  Google Scholar 

  40. 40

    Yu, W. J. et al. Highly efficient gate-tunable photocurrent generation in vertical heterostructures of layered materials. Nature Nanotech. 8, 952–958 (2013).

    ADS  Article  Google Scholar 

  41. 41

    Georgiou, T. et al. Vertical field-effect transistor based on graphene–WS2 heterostructures for flexible and transparent electronics. Nature Nanotech. 8, 100–103 (2013).

    ADS  Article  Google Scholar 

  42. 42

    Britnell, L. et al. Field-effect tunneling transistor based on vertical graphene heterostructures. Science 335, 947–950 (2012).

    ADS  Article  Google Scholar 

  43. 43

    Brinkmann, R., Derbenev, Y. & Flöttmann, K. A low emittance, flat-beam electron source for linear colliders. Phys. Rev. Spec. Top.-Ac. 4, 053501 (2001).

    ADS  Google Scholar 

  44. 44

    Piot, P., Sun, Y.-E. & Kim, K.-J. Photoinjector generation of a flat electron beam with transverse emittance ratio of 100. Phys. Rev. ST Accel. Beams 9, 031001 (2006).

    ADS  Article  Google Scholar 

  45. 45

    Peralta, E. A. et al. Demonstration of electron acceleration in a laser-driven dielectric microstructure. Nature 503, 91–94 (2013).

    ADS  Article  Google Scholar 

  46. 46

    Breuer, J. & Hommelhoff, P. Laser-based acceleration of nonrelativistic electrons at a dielectric structure. Phys. Rev. Lett. 111, 134803 (2013).

    ADS  Article  Google Scholar 

  47. 47

    McNeil, B. W. J. & Thompson, N. R. X-ray free-electron lasers. Nature Photon. 4, 814–821 (2010).

    ADS  Article  Google Scholar 

  48. 48

    de Abajo, F. J. G. Multiple excitation of confined graphene plasmons by single free electrons. ACS Nano 7, 11409–11419 (2013).

    Article  Google Scholar 

  49. 49

    Liu, S. et al. Coherent and tunable terahertz radiation from graphene surface plasmon polaritons excited by an electron beam. Appl. Phys. Lett. 104, 201104 (2014).

    ADS  Article  Google Scholar 

  50. 50

    Jablan, M., Buljan, H. & Soljacic, M. Transverse electric plasmons in bilayer graphene. Opt. Express 19, 11236 (2011).

    ADS  Article  Google Scholar 

Download references


The authors thank S. Shwartz, H. Buljan and L. Schächter for helpful discussions of aspects related to this work. The work was supported by the US Army Research Laboratory and the US Army Research Office through the Institute for Soldier Nanotechnologies (contract no. W911NF-13-D-0001), and the Science and Engineering Research Council (SERC; grant no. 1426500054) of the Agency for Science, Technology and Research (A*STAR), Singapore. The research of I.K. was also partially supported by the Seventh Framework Programme of the European Research Council (FP7–Marie Curie IOF) under grant agreement no. 328853 – MC–BSiCS.

Author information




All authors discussed the results and made critical contributions to the work.

Corresponding authors

Correspondence to Liang Jie Wong or Ido Kaminer.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 2053 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Wong, L., Kaminer, I., Ilic, O. et al. Towards graphene plasmon-based free-electron infrared to X-ray sources. Nature Photon 10, 46–52 (2016).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing