Vertical-cavity surface-emitting lasers: near to far-field anomalies due to spatially incoherent, amodal emission

A strong reduction of spatial coherence of the emission of large aperture vertical- cavity surface-emitting lasers occurs when they are driven by microsecond electrical pulses. The spatial decoherence manifests itself in the formation of a Gaussian far field intensity dis-tribution. The coherence radius we extract from the beam divergence is 1.4 micrometers. We will in this contribution first show the changes in the degree of coherence when going from CW to pulsed operation and then demonstrate the marked influence it has on the propagation and far-field properties. We will compare the experimental propagation with calculations based on a novel coherent mode expansion and show the good quantitative agreement