Long-resonator laser-diode bars for efficient kW emission

Abstract

High power diode lasers in the 9xx nm wavelength range are required for application in material processing, such as metal cutting and welding, either directly or as pump sources for solid state or fiber lasers. For example, continuous wave (CW) 1-cm diode laser bars are used for economic pumping of disk lasers [1] and continually improved optical output powers P, power conversion efficiency η E = P/IV (diode current I, voltage V) and far field angle are required. Research mainly focuses on three aspects: epitaxial designs for high η E > 60% at P ≥ 1 kW [2-4], low beam divergence and technology for low thermal resistance, low-stress packaging [1]. We here present progress in high fill-factor bars with long resonators, L = 4 and 6 mm, currently developed at the FBH for improved performance at P ≥ 1 kW. Higher L is beneficial as it reduces both the electrical (R s ) and thermal (R th ) resistances, as needed for delivering both high η E and P, especially in CW applications. Large L, however, commonly degrades threshold current and slope efficiency S = dP/dI due to increased optical loss α i ×L (partially addressable via facet reflectivity optimization), which can eliminate the benefit from low R s , R th . The larger chip area A also increases risk of loss in η E and P due to low emission homogeneity and polarization purity.