Research on New Concept Technology for Miniaturized Free Electron Lasers Has Made Important Progress

Free electron laser is known as the fourth generation light source and can provide high brightness coherent radiation from far infrared to X-ray. It has unprecedented revolutionary application value in fields such as physics, chemistry, materials science and life science. Traditional free electron lasers generate high-energy electron beams based on radio frequency accelerators, and then use an undulator composed of periodically arranged magnets to perform torsion and modulation of the electron beams, and finally emit high-intensity coherent radiation. Whether it is a radio frequency electron accelerator or an electronic undulator composed of periodic magnets, it is bulky and expensive. The development of a compact, low-cost new generation of free electron lasers, including table-top electron accelerators and undulators, is a major goal that the scientific community has been dreaming of chasing.

The State Key Laboratory of Laser Physics of the Shanghai Institute of Optics and Lasers has been making unremitting efforts to explore new principles and new concepts in the development of super-ultra-short laser driven table-top high-energy electron accelerators and undulators. Following the major achievement of a record high-brightness, high-quality electron beam in the electron acceleration of a super-ultra-short laser driven laser wake field in 2016, the research team has developed a new miniature, transient undulator driven by a super-ultra-short laser. In terms of conceptual research, we have made significant and original breakthroughs. For the first time, we have successfully built an all-optically driven wire waveguide spiral undulator and achieved a strong THz radiation output. In this work, the researchers used a beam of super-ultra-short laser to irradiate the metal wire target, and the directional high-energy electron emission was generated by the interaction between the laser and the plasma. At the same time, a very strong moment was generated on the wire based on the charge separation. Radial transient electric field; the electric field guides a large amount of high-energy electrons emitted along the direction of the wire to travel along the wire and perform a periodic spiral motion—corresponding to the spiral motion of the electron beam in a micro undulator. This movement produces strong THz radiation with conversion efficiency of more than 1%. In the experiment, the electron beam energy is ~100 keV, and the transient undulator cycle is about 650 micrometers. By changing the diameter of the wire, the radial electric field intensity can be changed, thereby changing the undulator cycle, and obtaining a frequency-tunable near-period broadband THz radiation. By changing the length of the wire, the non-linear amplification effect of the THz radiation intensity with the transmission distance was first observed, and the magnification was more than 10 times. This strong THz radiation source is expected to gain important applications in the detection of materials. In this study, both the electron beam and the undulator were produced by the same laser beam. The new concept of this undulator is expected to be further expanded and has been applied in short wavelength and even X-ray free electron lasers.

The reviewers highly praised this achievement and pointed out that “This paper describes a new method for generating high-energy quasi-periodical THz pulses.... This concept is amazing...it is an important and efficient way to generate THz. The new method.” “This paper not only clarified the dependence of experimentally produced THz radiation spectrum on the diameter of the wire, but also elucidated the cause of THz radiation.... This article will attract including lasers, electrokinetics (THz waves), Interest from researchers in the fields of electron beam, undulator, and free electron laser."

In this study, Liu Weiwei and others from Nankai University provided advanced testing equipment for the measurement of THz radiation and conducted related experiments in cooperation.

The study was supported by projects supported by the National Natural Science Foundation of China and the Class B Special Project of the Chinese Academy of Sciences.

(Original Title: Development of New Conceptual Research on Miniaturized Free Electron Laser Driven by Super-strong Ultrashort Lasers)