An analysis of surface-emitting terahertz quantum-cascade lasers operating at wavelengths near 100 /spl mu/m is presented. The devices use distributed feedback through second-order Bragg metal gratings to generate strong emission of radiation normal to the laser surface. The analysis is based on coupling between the exact Floquet-Bloch eigenmodes of infinite periodic structures in finite length devices. The results show performance of surface-emitting terahertz lasers comparable to edge-emitting devices, with high radiative efficiencies and low threshold gains. Using phase-shifts in the grating, high-quality single-lobe beams in the farfield are obtained.
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Schubert et al. (2006) studied this question.
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