Diffraction-Limited GaAs Laser with External Resonator

To obtain diffraction-limited radiation, a GaAs injection laser of 185 micro width was operated with an external resonator. The measured far-field radiation of this laser appears to be mainly in the lowest order transverse mode over nearly the entire width of the p-n junction. The peak radiated power at room temperature is 2.2 W and the external quantum efficiency is 0.031. The external resonator of the diffraction-limited GaAs laser has spherical symmetry although the lasing junction is asymmetrical and no mode-selecting iris is included. The operation of the GaAs laser with the external resonator resulted in a radiance increase of more than one magnitude.