Spatially resolved characterization of the coherence area in the incoherent emission regime of a broad-area vertical-cavity surface-emitting laser

We present direct measurements of the spatial coherence area of a pulsed broad-area vertical-cavity surface-emitting laser using a reversing wavefront interferometer. With this technique, we can assess the size and uniformity of the coherence area across the laser aperture, being of importance for projection applications. We show that the output beam can be considered quasi-homogeneous and that the measured coherence area corresponds well with the coherence area deduced from the far-field emission profile. We demonstrate that the coherence area is limited in size by the radial temperature gradient in the device and discuss the origin of coherence variations.