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Widely tunable electron bunch trains for the generation of high-power narrowband 1–10 THz radiation


Terahertz radiation enables the coherent excitation of many fundamental modes, such as molecular rotation, lattice vibration and spin precession. To excite the transient state of matter far out of equilibrium, high-power and tunable narrowband terahertz radiation sources have been in great demand for years. However, the terahertz source available at present cannot meet these tunability and power demands, leaving a large scientific gap that has yet to be fully explored. Here we convert the energy modulation induced by the nonlinear longitudinal space charge force to a density modulation and experimentally demonstrate the generation of electron bunch trains with modulation frequencies that are adjustable between 1 and 10 THz. The electron bunch trains can be directly used to produce tunable high-power narrowband terahertz radiation that fully covers the long-standing ‘terahertz gap’, which will open up many more possibilities in terahertz science.

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Fig. 1: Experimental demonstration of electron bunch trains.
Fig. 2: Bunching factor measurements.
Fig. 3: Measured longitudinal density distribution and projected density profile of the bunch trains.
Fig. 4: Terahertz measurements and simulations.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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This work was supported by the National Natural Science Foundation of China (NSFC grant no. 11835004).

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Authors and Affiliations



Y.L., L.Y. and C.T. conceived and designed the experiments. Y.L. conducted the experiments with the help from Z.L., Q.T., T.L., X.L., Y.D., J.S. and C.C. The simulations on beam dynamics were performed by Y.L. The manuscript was written by Y.L. with contributions from Z.L., L.Y., R.L., W.H. and C.T. Management and oversight of the project was provided by L.Y. and C.T.

Corresponding author

Correspondence to Lixin Yan.

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Nature Photonics thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1

Scheme for drive laser pulse train generation and measurements.

Supplementary information

Supplementary Information

Contents: (1) laser pulse width optimization and measurements; (2) linearization of energy chirps with an X-band harmonic cavity. Supplementary Figs. 1 and 2 and Supplementary Table 1.

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Liang, Y., Liu, Z., Tian, Q. et al. Widely tunable electron bunch trains for the generation of high-power narrowband 1–10 THz radiation. Nat. Photon. 17, 259–263 (2023).

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