Terahertz (THz) electromagnetic waves are between millimeter wave and infrared light, is a not yet fully recognized and utilized frequency band. Terahertz science and technology have gained rapid development in the past two decades and research in applied fields is also being carried out extensively. However, due to the lack of a suitable THz light source, especially the THz laser light source with tunable monochromatic large frequency range, the development of relevant research directions is restricted.
THz light can be generated based on laser technology, electron radiation, and the like. In the field of optics, the THz quantum cascade lasers have been rapidly developed in recent years, but their power, limited by frequencies from hundreds of microwatts to watts, has a very limited tuning range and the required low temperature The operating environment is also one of the factors that limits its widespread use. Accelerator-based THz electronic radiation source with high power characteristics, but its large-scale devices, high cost, it is difficult to universal. The development of compact and even portable THz radiation sources with high power and adjustable large frequency range is an important frontier in related research fields, but the current international progress is slow.
Since mid-2015, under the leadership of Professor Lu Yalin, the National Synchrotron Radiation Laboratory "Advanced THz Technology Task Force" has been set up. This task force combines the technical strengths of the National Synchrotron Radiation Laboratory, concentrates the key laboratory technology and gives full play to the team In the near future, a series of research progresses have been made on the theoretical research and key technologies around the theme of "compact THz electron radiation source".
In the aspect of continuous wave THz radiation, the group uses its specific Smith-Purcell effect to enhance the energy conversion efficiency between electron beam and radiation, and then proposes a method that can generate W-level radiation power based on mature electron source technology , The frequency can reach 1.5 THz Aurora radiation source program. This paper was published in Applied Physics Letters, 108, 183510 (2016) (full text link:
Figure 1: Schematic diagram of the THz ORA tube plan and radiated power
In order to obtain a higher power continuous wave THz radiation source, the research group proposed a THz tail-field radiation free-electron laser harmonic generation technology capable of generating a THz radiation source of the order of kW based on a well-proven, movable high-voltage DC gun . This paper was published in Optics letters, 46 (11), 2458, (2016) (Full Text Link:
Figure 2: Longitudinal electric and radiation spectra of THz wakefield radiation
In terms of the THz source with continuously tunable radiating frequency, the research group proposed a compact (full-duplex) technology based on the technology of laser pulse stacking and high-quality electronic pulse train generation Length of about 3 meters), high-power (MW pulse power), a wide range of continuous tunable (0.5-5.0 THz) pre-beam THz free electron laser radiation source program. The paper was published in Journal of Infrared, Millimeter, and Terahertz Waves, 2016, DOI: 10.1007 / s10762-016-0258-9 (full text link:
Figure 3: Pre-beam THz free electron laser radiation source plan
In order to overcome the limitation of microwave electron gun-based radiation source in generating low frequency (0.5 THz or less), high repetition rate and miniaturized light source, the research group used non-relativistic electron pulse train by laser pulse-triggered DC cathode gun to pass By adjusting the repetition frequency of electron impulses and selectively activating different high-order modes of the slow-wave structure, a small and high repetition frequency radiation source with adjustable radiation frequency of 0.1-1.0 THz is proposed by utilizing the characteristics of non-relativistic electron beam velocity. . This paper was published in Optics Express, 24 (4), 4109, (2016). (Full text link:
Figure 4: Radiation frequency range and radiant power of a pre-beam radiation source based on a DC gun
At the same time, the relevant research technology has applied for five Chinese invention patents. The research group is continuing to deepen the study of key principles and technologies and provide the key principles and technical reserves for future planning, development and construction of large scale free electron laser devices in the low-energy region in Hefei.
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