Terahertz Waves Emission From Two <formula formulatype='inline'><tex Notation='TeX'>$\hbox{Bi}_{2}\hbox{Sr}_{2} \hbox{CaCu }_{2} \hbox{O} _{8}$</tex></formula> Mesas in Series

The dependence of terahertz (THz) emission power on the thickness of series $\hbox{Bi}_{2}\hbox{Sr}_{2} \hbox{CaCu }_{2} \hbox{O} _{8}$ (BSCCO) mesas is studied in this letter. An intrinsic Josephson junction (IJJ) array with two BSCCO mesas in series is proposed. The current–voltage characteristics of the IJJs, the powers, and Fourier spectra of the THz emission are measured for different thicknesses of the mesas, which is gradually mounted by the argon ion beam milling. Experiment results indicate that the THz emission power grows as the thickness of the mesas is increasing. The power reaches a maximum value of about 0.502 $\mu\hbox{W}$ at a frequency of 0.708 THz when the thickness is 1200 nm. However, the THz emission power decreases while the thickness of the mesas keeps increasing. This nonlinearity between the THz emission power and the thickness of the mesas is due to the cavity resonance of the mesas and the self-heating generated by the IJJs in the mesas. The structure of connecting two mesas in series can be extended to form an IJJ array of multiple series mesas, which could further improve the THz emission power.