Spectrally resolved near-field images of unstable resonator diode lasers and their application to the measurement of refractive index

Lateral variations in refractive index play an important role in controlling the behavior of semiconductor lasers and amplifiers. In unstable resonator semiconductor lasers that contain a parabolic effective-index variation in the lateral direction, the strength of this index variation controls the radius of the cylindrical lasing modes, and thus affects other important characteristics such as threshold, efficiency, beam size and spatial coherence at high power. It is of prime importance to be able to measure the actual lateral index variation in semiconductor devices (especially under normal operating conditions). The technique demonstrated here allows direct measurement of the actual lateral index profile and can reveal deviations as caused by process variations, thermal effects, carrier non-uniformity and material non-uniformities.