Surface-emitting quantum-cascade lasers with a grating formed by focused ion beam milling

The results of studies of 7.5–8.0 $\mu$m range surface-emitting ring quantum-cascade lasers are presented. A second-order diffraction grating with a calculated coupling coefficient of $\sim$9 cm$^{-1}$ is formed on the entire surface of the ring cavity by focused ion beam milling. Surface-emitting lasing at room temperature near 7.75 $\mu$m with a threshold current density of $\sim$8 kA/cm$^2$ and an outer radius of the ring cavity of 202 $\mu$m is demonstrated. The results of studying the intensity distribution in the far-field near the normal to the surface showed the presence of two maxima. It is shown that the implemented coupling coefficient is not sufficient to ensure single-mode lasing in the studied ring quantum-cascade lasers.