Directional emission and universal far-field behavior from semiconductor lasers with limaccedilon-shaped microcavity

We report experimental demonstration of directional light emission from limaccedilon-shaped microcavity semiconductor lasers. Quantum cascade lasers (QCLs) emitting at lambda approximate to 10 mu m are used as a model system. Both ray optics and wave simulations show that for deformations in the range 0.37 < 0.43, these microcavities support high quality-factor whispering gallerylike modes while having a directional far-field profile with a beam divergence theta approximate to 30 degrees in the plane of the cavity. The measured far-field profiles are in good agreement with simulations. While the measured spectra show a transition from whispering gallerylike modes to a more complex mode structure at higher pumping currents, the far field is insensitive to the pumping current demonstrating the predicted universal far-field behavior of this class of chaotic resonators. Due to their relatively high quality factor, our microcavity lasers display reduced threshold current densities compared to conventional ridge lasers with millimeter-long cavities. The performance of the limaccedilon-shaped QCLs is robust with respect to variations of the deformation near its optimum value of epsilon=0.40.