Modeling of spatially incoherent laser emission

Recently we have developed a technique to drive some types of semiconductor lasers into a regime of spatially incoherent laser emission. This high-power, spatially incoherent emission regime is quite uncommon for lasers but can be useful in illumination and projection systems. A major drawback when using lasers in such illumination and projection systems is the appearance of speckle. This speckle is a random interference pattern that will be perceived by a (human) observer as a granularity or noise in the projected images, which is very disturbing. As speckle is due to the coherence properties of a beam, our technique to reduce the low degree of spatial coherence greatly helps to reduce speckle. The goal in this project is to model and understand the spatially incoherent laser emission regime.

The challenge of this modeling is that most laser models discussed in literature start from a modal decomposition of the electromagnetic field in the laser cavity.  Such an approach is not well suited to describe the spatially incoherent laser emission as in that case the emission no longer consists of a superposition of transverse modes. Instead, the laser acts as a partially coherent source with a Gaussian shaped complex degree of spatial coherence. The incoherent emission can be considered emission in multiple, independent, spatially separated coherence islands. Therefore the goal of this thesis is to construct a spatio-temporal laser model that reproduces our experimental findings. The model will not only be used to obtain a better insight of the physical processes that instigate the spatially incoherent emission, but we will also use it to optimize laser structures for their use in novel applications.

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