Terahertz gyrotrons with quasi-regular cavities
We describe two ways of the use in high-harmonic gyrotrons of quasi-regular cavities with short irregularities formed by the widening of cavity radius. The first one is a significant improvement of the selectivity of the second-harmonic gyrotrons due to the supression of parasitic near-cutoff fundamental-harmonic waves. The second approach is aimed to solve a typical problem of weakly-relativistic high-harmonics gyrotrons, namely, the use of long cavities ensuring extremely high diffraction Q-factors and a great share of Ohmic losses. We propose a quasi-regular cavity with periodic phase correctors, where a far-from-cutoff axial mode with a decreased diffraction Q-factor is excited in a gyrotron-like regime.
Sub-THz gyrotrons with special functions of frequency control for applications to DNP-NMR spectroscopy
Sub-THz gyrotrons with the functions of frequency control are useful for application to high power sub-THz spectroscopy including a DNP enhanced high-sensitive NMR spectroscopy. Continuous frequency tunability, frequency modulation and frequency step-changing will be achieved for our Gyrotron FU CW Series and such special functions of frequency control are applied for additional enhancement of NMR sensitivity. In this paper, it will be presented how such functions are achieved and how about the advantages of them for sensitivity enhancement of NMR spectroscopy.
Free Electron Lasers as a High-power Terahertz Sources
Free electron lasers (FEL) are the lasers which utilize the phenomenon of stimulated undulator radiation. Now they are the most powerful sources of electromagnetic radiation with frequency tunable from 1 to 10 THz. Contrary to most lasers, motion of an electron in the FEL may be described by classical mechanics and classical electrodynamics. Therefore they belong to the family of vacuum electronic devices, such as traveling wave tubes or klystrons. The basics of the FEL physics are discussed. General considerations are clarified through some examples. The Novosibirsk THz FEL is described briefly.