To obtain higher power P and frequency f emissions from the intrinsic Josephson junctions in a high-Tc superconducting Bi2Sr2CaCu2O8+δ single crystal, we embedded a rectangular stand-alone mesa of that material in a sandwich structure to allow for efficient heat exhaust. By varying the current-voltage (I-V) bias conditions and the bath temperature Tb, f is tunable from 0.3 to 1.6 THz. The maximum P of a few tens of iW, an order of magnitude greater than from previous devices, was found at Tb ~ 55 K on an inner I-V branch at the TM(1,0) cavity resonance mode frequency. The highest f of 1.6 THz was found at Tb = 10 K on an inner I-V branch, but away from cavity resonance frequencies. A possible explanation is presented. [ABSTRACT FROM AUTHOR]