# The Gyrotrons as Promising Radiation Sources for THz Sensing and Imaging
## 4 Conclusions and Outlook  
Nowadays, we are witnessing spectacular progress in the broad fields of the terahertz science and technology stipulated by the remarkable advancements in the development of the fundamental triad: sources, detectors, and methods. Each of them stimulates both the improvement and further evolution of the other two, and together, these three basics generate a synergy effect leading to the emergence of novel devices, methods, and applications. As the most powerful sources of coherent radiation in the sub-THz and THz frequency range operating in both pulsed and CW regimes, the gyrotrons have demonstrated a remarkable potential for bridging the so-called THz gap and have opened the road to many novel applications in the fundamental physics research and applied sciences. In this review, the advantages of the gyrotrons as versatile radiation sources have been presented and illustrated with an emphasis on some of the most notable and well established as well as emerging technologies. The selected examples reveal both the current state-of-the-art of their development and bring to light the main trends for further improvements in their operational performance and functionality.  
Taking into account the active research on the gyrotron development worldwide, the accumulated experience, and knowledge, we anticipate a continuation of the progress in this field. It is believed that this will lead not only to the proliferation of the existing applications that rely on the gyrotrons as radiation sources but will stimulate also the emergence of novel yet unknown approaches, methods, and devices. Definitely among them will be such that are related to imaging, sensing, quality control, etc. The ultimate goal of the present review paper was to inform the researchers working on these important applications about the capabilities of the gyrotrons as appropriate radiation sources. We hope that such an overview would be helpful in their work.  
[PERSON] and [PERSON] conceived the idea to prepare a review paper for the special issue on \"Teraehrtz Sensing and Imaging\" that presents the potential of the gyrotrons as promising radiation sources in this field. [PERSON], [PERSON], [PERSON], and [PERSON] provided the materials and participated equally in the discussions on the topics covered in the review. [PERSON] wrote the manuscript with support from [PERSON], [PERSON], and [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research was funded by IAP-RAS (Institute of Applied Physics of the Russian Academy of Sciences), grant number 0035-2019-0001. The APC was funded by Gyro Tech Co., Ltd., Japan.  
The work has been carried out in the framework of the collaboration of the International Consortium for Development of High-Power Terahertz Science and Technology (visit: [[http://ir.u-fukui.ac.jp/](http://ir.u-fukui.ac.jp/)]([http://ir.u-fukui.ac.jp/](http://ir.u-fukui.ac.jp/)) Website_Consortium) organized and facilitated by the Research Center for Development of Far-Infrared Region at the University of Fukui, and supported by Gyro Tech Co., Ltd., Fukui (Japan). The work of the Russian team has been supported under the project 0035-2019-0001.  
The authors declare no conflict of interest.