Development of high frequency Gyrotrons in FIR FU covering sub-THz to THz range for applications to high power THz spectroscopy

Powerful sources of coherent radiation in the sub-terahertz to terahertz frequency range are required for expanding number of applications in the physical research and in various advanced high power THz technologies. In recent years, a spectacular progress in the development of various gyro-devices and in particular, the powerful high frequency (sub-terahertz to terahertz) gyrotron oscillators has demonstrated a remarkable potential for bridging the so-called terahertz power gap and stimulated many novel and prospective applications. In this paper, we outline two series of such gyro-devices, namely the Gyrotron FU Series which includes pulsed gyrotrons and Gyrotron FU CW Series which consist of CW (continuous wave) or long pulse gurotrons. Both series are developed at Research Center for Development of Far Infrared Region, University of Fukui (FIR FU). We present the most remarkable achievements of these devices and illustrate their applications by some characteristic examples. An outlook for the further extension of the Gyrotron FU CW Series is also provided.