Rattunde, MarcelMarcelRattundeHoll, PeterPeterHollWagner, JoachimJoachimWagner2022-05-062022-05-062022https://publica.fraunhofer.de/handle/publica/41650410.1002/9783527807956.ch3This chapter provides a basic overview of mid-infrared (MIR) vertical external-cavity surface-emitting lasers (VECSELs) based on the (AlGaIn)(AsSb) materials system and introduces key developments concerning conversion efficiency and output power as well as single-frequency operation (SFO) and tunability of such laser sources. Beside the GaSb-based VECSELs, there exist a plurality of semiconductor-based laser sources for the MIR wavelength range, each with its own strength and weaknesses and specific performance limitations. The chapter reviews the different VECSEL-chip mounting technologies and output power levels that can be reached for the different designs and mounting options. The most widely used general structural layout for GaSb-based VECSEL in the 2-3 mm wavelength range is a barrier pumped structure. The VECSEL concept combines several features, which are advantageous for low-noise SFO. Using GaSb-based VECSEL chips with different mounting techniques, a variety of setups for SFO have been demonstrated, all with different strength and weaknesses.en667book article