Long-wavelength (λ=10 μm) quadrupolar-shaped GaAs-AlGaAs microlasers

In this paper, we present experimental results of our investigations on deformed GaAs-AlGaAs microlasers emitting around lambda = 10 mu m. These quantum cascade lasers exhibit interesting features regarding the threshold current densities, optical output, and far-field pattern, A slight aberration from a circular cross section decreases the threshold current density for microlasers (which have a radius of 50 mu m). For larger deformations is an element of, the threshold starts to increase because of the increasing mirror losses. For smaller microlasers (radii between 22 and 33 mu m), the threshold current density increases already for slight deformations due to the increase of the mirror losses. The experimental results can be fitted very well with the mirror losses as a fitting parameter using a well-known and simple model. Threshold currents as low as 170 mA are measured for a cylindrical microlaser with a radius of 22 mu m, The peak optical output is increasing quasi-esponentially with rising deformation, Lasing emission from slightly concave resonator shapes is detected. The bow-tie mode and other modes-different from Whispering-gallery modes-are responsible for highly directed emission along the diagonal axis and along the short axis, respectively, of the microlasers. Single-mode emission with a side-mode suppression ratio larger than 25 dB is shown over the entire drive current range for a highly deformed microlaser, The laser line can be temperature tuned with Delta v/T = -0.027 cm(-1)/K. A dual mode sw itching depending on the drive current with a mode spacing of Delta v = 8.1 cm(-1) between 999 and 1007.1 cm-l is observed for a less deformed microlaser.