Spectroscopic techniques for an in situ analysis of vertical-external-cavity surface-emitting lasers are presented and exemplary results are discussed. Spatially resolved photoluminescence is shown to provide access to the temperature distribution inside the active area of the laser chip. Both the shape and the size of the pump spot are found to strongly influence the thermal properties and the output power of the device. In addition, the temporal stability of a laser emitting at two distinct wavelengths is studied using single-shot streak-camera measurements. The collected data is evaluated via quantitative statistical analysis schemes identifying stable and unstable regimes of operation.