Vertical external-cavity surface-emitting laser based on a novel GaInP/AlGaInP grating waveguide for efficient high-power operation

多用途半导体盘状激光器的功率调节仍然是一个挑战，特别是对于具有GaInP/AlGaInP材料系统的红色光谱区域。这种增益结构对温度效应非常敏感，需要腔内冷却以绕过厚的、导热性能差的DBR反射镜。通过井内抽水来降低热负荷已被证明是非常有效的。然而，当与腔内冷却结合使用时，需要外部复杂的多通道光学器件来有效地吸收泵浦辐射。我们的目标是通过用有源光栅波导结构(GWS)取代带有DBR的半导体盘来绕过这些限制，并首次展示基于光栅波导的GaInP VECSEL在红色光谱范围内的性能。因此，光栅波导应具有以下特性：-激光模式的高反射率和泵浦辐射的耦合效率，-增强的激光跃迁增益和增强的泵浦辐射的吸收系数，-在谐振器外部的散热器，但接近QW/QD层，以实现有效的冷却。高对比度栅格或弱耦合谐振型波导栅格。不同的偏振状态和/或波长可以用二维光栅(光子晶体)来寻址。由于这是一个全新的领域，我们将通过设计、建模、技术(外延、光栅制造)和实验(光谱和激光表征)之间的反馈回路，分几个连续步骤探索最有希望的设计：-高反射无源器件，-QW或QD包含有源器件，以及-全功能激光结构(GWS VECSEL)，粘合到钻石散热器上。

Power scaling with versatile semiconductor disk lasers is still a challenge, especially for the red spectral region with the GaInP/AlGaInP material system. The gain structure is quite sensitive to temperature effects and requires intra-cavity cooling to bypass the thick, poorly heat-conducting DBR mirror. Reducing the heat load by in-well pumping has been shown to be very effective. However, when used in combination with intra-cavity cooling, external complex multi-pass optics with many passes for efficient pump-radiation absorption is needed.Our objective is to circumvent these limitations by replacing the semiconductor disk with DBR by an active grating waveguide structure (GWS) and – for the first time – to demonstrate a grating-waveguide-based GaInP VECSEL in the red spectral range. Therefore, the grating waveguide should have the following characteristics:– highly reflective for the laser mode and efficient for coupling of the pump radiation,– enhanced gain at the laser transition and enhanced absorptance of the pump radiation,– heatsink outside the resonator, but close to the QW/QD layers, for effective cooling.There are several options to realize these requirements with various trade-offs, eg. high-contrast gratings or weakly coupled resonant waveguide gratings. Different polarization states and/or wavelengths can be addressed with two-dimensional gratings (photonic crystals). Since this is quite new territory, we will explore the most promising designs in several consecutive steps with feedback loops between design, modeling, technology (epitaxy, grating fabrication), and experiment (spectroscopic and laser characterization):– Highly reflective passive devices,– QW or QD containing active devices, and– A fully functional laser structure (GWS VECSEL), bonded to a diamond heat spreader.