We describe the fabrication and operation of surface emitting second-order distributed feedback quantum cascade ring lasers. The devices exhibit single-mode emission at a wavelength of 3.95 μm with a side mode suppression ratio of 25 dB. A linear tuning coefficient of 0.13 cm~(-1)/K is observed. A single longitudinal mode in the ring shaped resonator results in a highly symmetric far-field pattern and a low beam divergence, represented by a full width at half maximum of ～3°. Based on these characteristics the presented compact coherent light source may find its way into today's midinfrared spectroscopy applications.
展开▼
