Mesa-Sidewall Effect on Coherent Terahertz Radiation via Spontaneous Synchronization of Intrinsic Josephson Junctions in Bi2Sr2CaCu2O8+δ

We investigate the effect of the Bi2Sr2CaCu2O8+delta mesa sidewall on the spontaneous synchronization of intrinsic Josephson junctions and concomitant terahertz radiation. We develop a lithography technique to control the sidewall angles. Using a Fourier interferometer, we characterize the radiation emitted from a series of mesas with different sidewall angles. We determine that a uniform distribution of the oscillation frequencies is essential to produce coherent radiation outside the mesa. It is also noted that in the resonant state, the input excess energy is transferred to the excitation of the coherent state.