We have demonstrated an optically pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) generating more than 20 W of cw output power in a fundamental transverse mode (M2 approximately 1.1) at 960 nm. The laser is highly efficient with a slope efficiency of 49%, a pump threshold of 4.4 W, and an overall optical-to-optical efficiency of 43%.
We have studied the effects of various conditions of rapid thermal annealing ͑RTA͒ on 10 nm GaInNAs/ GaAs single quantum wells ͑SQWs͒ with fixed indium concentration and increasing nitrogen content to obtain photoluminescence ͑PL͒ in the telecom wavelength regime of 1.3 and 1.5 m. Specifically, we analyzed the results of annealing for a fixed short time but at different temperatures and for longer times at a fixed temperature. In all experiments, InGaAs SQWs with the same In concentration were used as references. For both RTA conditions, the well-known blueshift of the band gap energy and the PL intensity improvement show trends that reveal that these are unrelated effects. At high RTA temperatures the PL efficiency reaches a maximum and then drops independently of N content. On the contrary, the blueshift experiences a rapid increase up to 700°C ͑strong blueshift regime͒ and it saturates above this temperature ͑weak blueshift regime͒. Both these blueshift regimes are related to the nitrogen content in the SQWs but in different ways. In the strong blueshift regime, we could obtain activation energy for the blueshift process in the range of 1.25 eV, which increases with N content. Analysis with high-resolution x-ray diffraction ͑HRXRD͒ shows that the blueshift experienced in this regime is not due to a stoichiometric change in the QW. In the weak blueshift regime, the blueshift, which is only partly due to In outdiffusion, saturates more slowly the higher the N content. Annealing at the same temperature ͑600°C͒ for a longer time shows that the blueshift saturates earlier than the PL intensity and that samples with higher nitrogen experience a larger blueshift. Only a small In outdiffusion for annealing at high temperatures ͑Ͼ650°C͒ and long duration was observed. However, this modest stoichiometric change does not explain the large blueshift experienced by the GaInNAs SQWs. We conclude that the mechanism responsible for the drastic blueshift after annealing is related to the N content in the QW, while the improvement in PL integrated intensity is uniquely related to the annealing conditions.
GaInNAs 1.3-μm quantum-well saturable absorber mirrors are characterized with spectrally resolved nonlinear reflectivity measurements over 70nm around the broadened band edge. All important parameters such as saturation fluence Fsat, modulation depth ΔR, and nonsaturable loss ΔRns are obtained relative to the photoluminescence (PL) peak. Fsat has a minimum of 4μJ∕cm2 10nm above the PL peak and ΔR scales with the linear absorption even in the bandtail. The product ΔR∙Fsat important to suppress Q-switching instabilities in mode-locked lasers decreases linearly with wavelength and reaches a minimum 20nm above the PL peak. We observed wavelength-independent nonsaturable losses of only about 10% of the maximum linear absorption. These results increase the understanding of optical and electronic properties of GaInNAs around the band edge.
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