ABSTRACT
This chapter considers vertical external-cavity surface-emitting organic lasers (VECSOL), which are the organic counterparts of inorganic VECSELs. It reviews the main characteristics of laser emission that are directly linked to the macroscopic external cavity. The chapter explores how the empty space left between the two mirrors can be usefully employed to engineer the spectrum of the laser in three different ways that conduct to discussing several derivations of the VECSOL concept. Lasers based on solution-processed thin films have been demonstrated with many different materials and also with various designs for the laser resonator. In contrast, external cavities enable a better control of spatial mode matching between pump and cavity modes, the key enabler for a high beam quality and high conversion efficiency. The key for an efficient conversion of the pump radiation to the laser mode is a good spatial overlap between the pump spot and the desired laser mode of the cavity.
