High efficiency, 8W narrow-stripe broad-area lasers with in-plane beam-parameter-product below 2 mm mrad

High power diode lasers are the most efficient technology for converting electrical input power into optical output power. Their efficiency and low manufacturing cost lead to their being the preferred source for industrial material processing applications, where kilowatt-class diode laser systems are produced by combining the output of many diode lasers into an optical fibre, with a beam parameter product, B_PP, around 20-30 mm mrad [1]. Although this is sufficient for many applications, deep cutting of metals requires sources with B_PP <; 2 mm mrad, as delivered by fibre, solid state and CO₂ lasers. Sophisticated beam combination schemes can increase the overall power level of diode laser systems [1,2,3], but B_PP is ultimately limited by the semiconductor devices. A typical high power broad area laser used in a material processing system has a stripe width W = 90...100 μm and operates with a continuous wave output power, P_out = 10 W, an efficiency at the operation power, η_E(P_out) > 60% and an in-plane B_PP > 3 mm mrad [3]. Therefore, improved diode laser performance is required.