Abstract

Electromagnetic Waves at terahertz (THz) frequencies are indispensable not only for the basic research but also a variety of applications such as environmental sensing, imaging, molecular identification, drag and explosive detection, pharmaceutical screening, biological and medical use, ultrafast communications, etc. However, such applications at THz frequencies have been far from reality for a long time because a sharp gap in the frequency-power diagram centered around 1 THz, known as the “Terahertz gap”, could not be overcome in the history of electromagnetic wave generation.

In 2007, the discovery of the coherent and continuous electromagnetic waves in the THz region from a large mesa structure made of high-Tc superconductor Bi2Sr2CaCu2O8+d by Ozyuzer et al. [1] shed a dim light on the issue of the terahertz gap. Since then, much effort has been concentrated not only on the basic understanding of the mechanism of THz emission from ～10^3 intrinsic Josephson junctions existing in the mesa but also on the development of higher power and higher frequency THz generation. We have just recently succeeded in generating a maximum frequency of 2.4 THz [2] and the power of 50 microwatt/mesa, and in operating at liquid nitrogen temperature [3].

I will give a short history of IJJ T Hz emitter development [4,5], then, the present status [6,7] and the future perspectives of the IJJ emitter, especially in comparison with the similar semiconducting devices such as resonant-tunneling diodes (RTDs) and quantum cascade lasers (QCLs) etc.

References L. Ozyuzer et al., Science 318 (2007) 1291. T. Kashiwagi et al., Appl. Phys. Lett. 107 (2015) 082601. H. Minami et al., J. Phys.: Condens. Matter 28 (2016) 025701. U. Welp, K. Kadowaki and R. Kleiner, Nature Photon. 7 (2013) 702. T. Kashiwagi et al., Phys. Rev. Applied 4 (2015) 054018. K. Nakade et al., Scientific Reports 6 (2016) 23178. K. Delfanazari et al., IEEE Trans. Terahertz Sci. & Technol. 5 (2015) 505.