Demonstration of direct-amplification enabled harmonic generation in an ultraviolet free-electron laser

H Hao Sun J Jitao Sun (Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,) L Li Zeng (The Institute for Advanced Studies (IAS), College of Chemistry and Molecular Sciences) Y Yifan Liang (Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory) L Lingjun Tu (Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,) H Huaiqian Yi (Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,) Q Qinming Li X Xiaofan Wang Y Yong Yu J Jiayue Yang (State Key Laboratory of Chemical Reaction Dynamics and Dalian Coherent Light Source, Dalian Institute of Chemical Physics) Z Zhigang He (F.M. Kirby Neurobiology Center, Boston Children’s Hospital) Y Yuhuan Tian (State Key Laboratory of Chemical Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences 2 , Dalian 116023,) L Likai Wang (School of Chemistry and Chemical Engineering) Z Zequn Wang (Key Laboratory of Materials Modification by Laser, Electron, and Ion Beams (Ministry of Education), School of Physics, Dalian University of Technology , Dalian 116024,) G Guorong Wu W Weiqing Zhang X Xueming Yang (State Key Laboratory of Chemical Reaction Dynamics and Dalian Coherent Light Source, Dalian Institute of Chemical Physics)

Abstract

We report the experimental demonstration of direct-amplification enabled harmonic generation in an ultraviolet free-electron laser (FEL) driven by a low-intensity seed laser. By employing a versatile undulator configuration that enables seed amplification and harmonic generation within a unified setup, we achieved over 100-fold energy gain of the seed and observed exponential growth at the second harmonic. The results demonstrate that a sufficiently long modulator cannot only amplify a weak seed but also induce strong energy modulation of the electron beam, enabling efficient harmonic bunching. This method markedly relaxes the power requirements on external seed lasers and presents a viable route toward high-repetition-rate, fully coherent FELs.

Article Details

Volume / Issue Vol. 127, Issue 18
Published November 03, 2025
ISSN 0003-6951
Publisher American Institute of Physics

Journal Info

Applied Physics Letters

American Institute of Physics

ISSN: 0003-6951 Physical Sciences

Authors (17)

H

Hao Sun

J

Jitao Sun

Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,

L

Li Zeng

The Institute for Advanced Studies (IAS), College of Chemistry and Molecular Sciences

Y

Yifan Liang

Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory

L

Lingjun Tu

Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,

H

Huaiqian Yi

Institute of Advanced Light Source Facilities 1 , Shenzhen, Shenzhen 518107,

Q

Qinming Li

X

Xiaofan Wang

Y

Yong Yu

J

Jiayue Yang

State Key Laboratory of Chemical Reaction Dynamics and Dalian Coherent Light Source, Dalian Institute of Chemical Physics

Z

Zhigang He

F.M. Kirby Neurobiology Center, Boston Children’s Hospital

Y

Yuhuan Tian

State Key Laboratory of Chemical Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences 2 , Dalian 116023,

L

Likai Wang

School of Chemistry and Chemical Engineering

Z

Zequn Wang

Key Laboratory of Materials Modification by Laser, Electron, and Ion Beams (Ministry of Education), School of Physics, Dalian University of Technology , Dalian 116024,

G

Guorong Wu

W

Weiqing Zhang

X

Xueming Yang

State Key Laboratory of Chemical Reaction Dynamics and Dalian Coherent Light Source, Dalian Institute of Chemical Physics