In the electromagnetic spectrum, a frequency band between the microwave and the infrared, the terahertz band, has been wearing a mysterious veil. The exposure of terahertz waves to the public is far less than the radio waves used by people, the microwaves used in life, the x-rays used in medicine, and the visible light that allows the eyes to distinguish the world. However, once the discovery of terahertz radiation, it has been hailed by international scholars as "one of the top ten technologies for changing the future world."
Terahertz radiation can effectively overcome some shortcomings that exist in imaging, medical, communications and other applications in other wavebands and has some advantages that are irreplaceable in the prior art. However, there are still many bottlenecks in the application of terahertz waves. One of them is that it is difficult to obtain a strong terahertz radiation source. At present, the most effective way to generate strong terahertz radiation is to use the high-energy electron beam in traditional accelerators to wiggle and modulate in an undulator made of periodically arranged magnets to generate high-intensity coherent radiation. However, the conventional linear accelerator and the electronic storage ring device are bulky and expensive, and developing a miniaturized next-generation radiation source has always been the dream target of the scientific community.
Recently, the State Key Laboratory of Strong Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, proposed a new concept of femtosecond laser driven wire waveguide spiral undulator. In cooperation with Nankai University Institute of Modern Optics, The scheme achieves a strong THz radiation output. The research was recently published at Nature Photonics [11, 242-246 (2017)].
Experiment, the use of a bunch of Asia-Pacific watt-class femtosecond intense laser irradiation and hair wire diameter equivalent to the target, by the strong interaction of the laser plasma generated directional high-energy electron emission due to charge separation effect, instantaneous on the wire Produce a very strong radial transient electric field; a large number of high-energy electrons emitted along the direction of the wire are guided by the radial electric field, transmitted along the wire and cyclical spiral movement - the equivalent of electron beam in a miniature Undulator in the spiral motion, while obtaining a non-linear amplification of the strong THz radiation output, the conversion efficiency of 1% or more, as shown in Figure 1.
Figure 1 femtosecond laser-driven wire-waveguide spiral waveguide produces strong terahertz radiation
In this work, the electron beam energy is about 100 keV and the undulator period is about 650 μm. Researchers change the diameter of the wire to change the strength of the radial electric field, thus changing the undulator cycle, get the frequency tunable strong terahertz radiation; by changing the length of the wire, the first observed terahertz radiation intensity with the transmission distance The amplification effect, magnification up to 10 times.
The all-optical driven micro-undulator developed in this study is a new type of undulator, and both the electron beam and the undulator are generated simultaneously by the same laser beam. The undulator is expected to be further expanded in the field of strong THz radiation, new light source and freedom Electronic lasers and other related fields have been widely used.
The paper reviewer believes that "the paper describes a new method of generating high-energy quasi-single-cycle THz pulses" and states "This study will attract a wide range of applications including lasers, electrodynamics (THz waves), electron beams, undulator and free Electronic laser and other fields of interest of researchers. "
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