RESUMO

As in a recent paper [I. Alvarado-Rodríguez, P. Halevi, and Adán S. Sánchez, Phys. Rev. E 63, 056613 (2001); 65, 039901(E) (2002)], we study the power emitted by an oscillating dipole in a superlattice (SL) modeled by means of a periodic distribution of Dirac-delta functions (Dirac-comb SL). However, while in the aforementioned paper the radiation was restricted to the transverse electric (TE) polarization mode, here we focus our attention on the transverse magnetic (TM) mode. Employing the same methodology, again we find that the power spectra are dominated by slope discontinuities. These occur - if at all - at the band edges for on-axis propagation, depending on the dipole's position and orientation. The largest enhancement or inhibition is present for normalized frequencies such that (omegad/c) less, similar 2pi; here, omega is the dipole frequency, c is the speed of light in vacuum, and d is the distance between the barriers. For substantial values of the grating strength considerable enhancement or suppression of the radiated power (in comparison to the free-space value) is obtained. We also find that the power emitted by a gas of randomly oriented dipoles exhibits slope discontinuities at all band edges for on-axis propagation. In comparison with the TE polarization case, the TM polarization exhibits several different qualitative features.