Role of thermal effects on the onset of spatially incoherent emission in a Broad-Area Vertical-Cavity Surface-Emitting Laser

We present an experimental study of the spatial coherence properties of broad-area vertical-cavity surface-emitting lasers (BA-VCSELs). In particular we demonstrate that the spatially incoherent emission regime that can be invoked in pulsed operation stems from two different thermal effects: thermal lens and thermal chirp. We have separately measured the influence of these effects on the appearance of the spatially incoherent emission by pre-installing a thermal lens through a current bias and subsequently modulating a pulse onto the bias.