Controlling the Emission Properties of High-Power Semiconductor Lasers: Stabilization by Optical Feedback and Coherence-Control

The output powers of semiconductor lasers (SLs) are significantly enhanced by increasing the emitting area of the devices. However, increasing the output power can lead to deteriorated static and dynamic emission properties of high power SLs. In this thesis, various controlschemes based on spatially and spectrally filtered optical feedback are presented which, both, improve the beam quality and stabilize the nonlinear spatiotemporal emission dynamics of broad-area SLs and of broad-area vertical-cavity surface-emitting lasers (BA-VCSEL). Next to the dynamic emission properties of high-power SLs, their spatial coherence properties can be manipulated, which is of particular interest for various applications. A drastic reduction of the spatial coherence is shown to result in fundamentally modified beam characteristics of a BA-VCSEL. Time-resolved measurements of the evolution of the emission are presented giving insight into the thermal mechanisms responsible for the loss of spatial coherence.