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تسجيل مستخدم جديدCavity mode identification for coherent terahertz emission from a nearly square stack of intrinsic Josephson junctions
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Stacks of intrinsic Josephson junctions in Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta }$ emit intense and coherent terahertz waves determined by the internal electromagnetic cavity resonance. We identify the excited transverse magnetic mode by observing the broadly tunable emissions from an identical nearly square stack and simulating the scattering spectrum. We employ a wedge-type interferometer to measure emitted integral power independently of the far-field pattern. The simulation results are in good agreement with observed resonance behaviors as a function of frequency.
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We show that shunt capacitor stabilizes synchronized oscillations in intrinsic Josephson junction stacks biased by DC current. This synchronization mechanism has an effect similar to the previously discussed radiative coupling between junctions, howe
ver, it is not defined by the geometry of the stack. It is particularly important in crystals with smaller number of junctions, where radiation coupling is week, and is comparable with the effect of strong super-radiation in crystal with many junctions. The shunt also helps to enter the phase-locked regime in the beginning of oscillations, after switching on the bias current. Shunt may be used to tune radiation power, which drops as shunt capacitance increases.
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We report on THz emission measurements and low temperature scanning laser imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the col
d part of the stack, coexist. By varying the hot spot size the cavity resonance frequency and the emitted radiation can be tuned. The linewidth of radiation is much smaller than expected from the quality factor of the cavity mode excited. Thus, an additional mechanism of synchronization seems to play a role, possibly arising from nonequilibrium processes at the hot spot edge.
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