Magnetic field effects on THz radiation from Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ mesa structures

In a previous our study, coherent and continuous electromagnetic radiation phenomena in mesa structures of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystal have been investigated precisely in magnetic fields up to only 150 Oe [1]. This experimental result showed that the emission intensity decreases sharply for the field parallel to the $c$-axis, while it decreases gradually as increasing magnetic field for the in-plane field. In order to improve the measurement, we developed a new system with a better angular resolution and much wider magnetic field range up to 6 T, and a mesa having much stronger THz emission power. The mesa structure is also changed to the stand-alone type of mesa, which produces higher power THz radiation with ideal distribution of radiation [2]. In this presentation, the recent detailed results will be shown in magnetic fields both parallel and perpendicular to the \textit{ab}-plane of Bi2212, where the Josephson and pancake vortices are playing an important role for THz radiation.\\[4pt] [1] K. Yamaki \textit{et al}., physica C \textbf{470} (2010) S804.\\[0pt] [2] T. Kashiwagi \textit{et al}., Jpn. J. Appl. Phys. \textbf{51} (2012) 010113.