Tunable terahertz emission from Bi2Sr2CaCu2O8 mesa devices

The so-called ``terahertz gap,'' covering frequencies from approximately 0.3 to 1.5 THz, is of particular interest for a number of scientific and security applications, although no bright sources of coherent radiation presently exist in this range. However, stacks of high-temperature superconducting intrinsic Josephson junctions are a promising candidate. [1] Here we discuss recent progress in improving the performance of these devices. In particular, we demonstrate that via control of bias voltage and operating temperature, the emission from an 80-$\mu $m wide Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ mesa can be tuned continuously over a frequency range in excess of 10{\%} in the vicinity of 0.5 THz. We find that as the emission frequency increases from 0.420 to 0.492 THz, the linewidth increases from $<$2.25 GHz (limited by instrument resolution) to $\sim $9 GHz. \\[4pt] [1] L. Ozyuzer et al., Science 318 (2007) 1291-1293.