Long-wavelength (lambda=10 mu m) quadrupolar-shaped GaAs-AlGaAs microlasers

In this paper, we present experimental results of our investigations on def ormed GaAs-AlGaAs microlasers emitting around lambda = 10 mu m. These quant um cascade lasers exhibit interesting features regarding the threshold curr ent densities, optical output, and far-field pattern, A slight aberration f rom a circular cross section decreases the threshold current density for mi crolasers (which have a radius of 50 mu m). For larger deformations is an e lement of, the threshold starts to increase because of the increasing mirro r losses. For smaller microlasers (radii between 22 and 33 mu m), the thres hold current density increases already for slight deformations due to the i ncrease of the mirror losses. The experimental results can be fitted very w ell with the mirror losses as a fitting parameter using a well-known and si mple model. Threshold currents as low as 170 mA are measured for a cylindri cal microlaser with a radius of 22 mu m, The peak optical output is increas ing quasi-esponentially with rising deformation, Lasing emission from sligh tly 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, o f 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.