Studies on the Gyrotrons as Promising Radiation Sources for THz Sensing and Imaging

The gyrotrons are powerful sources of coherent radiation that can operate in both pulsed and CW
(continuous wave) regimes. Their recent advancement toward higher frequencies reached the THz
region and opened the road to many new applications in the broad fields of high-power terahertz
science and technologies. Among them are advanced spectroscopic techniques most notably NMRDNP
(Nuclear Magnetic Resonance with signal enhancement through Dynamic Nuclear Polarization,
ESR (Electron Spin Resonance) spectroscopy, precise spectroscopy for measuring the HFS
(hyperfine splitting) of positronium, etc. Other prominent applications include materials processing
(e.g. thermal treatment as well as sintering of advanced ceramics), remote detection of concealed
radioactive materials, radars, biological and medical research, just to name a few. Among prospective
and emerging applications that utilize the gyrotrons as radiation sources are imaging and sensing for
inspection and control in various technological processes (for example food production), security, etc.
In this paper, we overview the current status of the research in this field and show that the gyrotrons
are promising radiation sources for THz sensing and imaging based on both the existent and
anticipated novel techniques and methods. 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.