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Characteristic features of terahertz radiation emitted from a rectangular mesa comprised stacked intrinsic Josephson junctions in the layered high-T c superconductor Bi 2 Sr 2 CaCu 2 O 8+␦ are reported. The emission with the total power of ϳ5 W at 0.63 THz shows a characteristic spatial distribution reflecting the rectangular shape. The stability of the emission was measured for at least 20 min. and the power fluctuation was found to be less than 4%. Furthermore, the radiation is highly polarized linearly with a ratio of 50:1. All features, including the spectral purity narrower than 4 GHz at full width at half maximum, promise a stable, coherent, and continuous terahertz source for various applications.

Highly crystalline corundum-structured -(Ga 1Àx Fe x ) 2 O 3 alloy thin films were fabricated on c-plane sapphire substrates by using a mist chemical vapor deposition method. The full-widths at half maximum of X-ray diffraction rocking curves were smaller than 100 arcsec for the entire range of x from 0 to 1. Optical band gaps were artificially tuned to a value between those of -Ga 2 O 3 and -Fe 2 O 3 , that is, 2.2 and 5.3 eV with changing the Fe content x in the films. Magnetic measurements revealed ferromagnetic properties of a -(Ga 1Àx Fe x ) 2 O 3 (x ¼ 0:24) thin film at 110 K.