Femtosecond surface-emitting lasers

Diode-pumped solid state lasers, long dominant in many high power applications, now face a challenge from optically-pumped semiconductor lasers, which add spectral versatility to the good beam quality and potential for power-scaling that are characteristic of optically-pumped disc lasers. The vertical-external-cavity surface-emitting semiconductor laser, or VECSEL, readily exhibits passive mode- locking with the inclusion of a semiconductor saturable absorber mirror ( SESAM) in the external cavity. These devices most often emit picosecond pulses, recruiting only a small fraction of the available gain bandwidth of the quantum wells. If the dispersive and filtering effects of the multilayer gain and saturable absorber structures are well- controlled, however, it is possible to observe clean sub- picosecond pulses of duration down to 100fs and below. The presentation will describe SESAM- mode- locked VECSELs based on compressively strained InGaAs/ GaAs quantum wells that generate trains of near- transform- limited femtosecond pulses at wavelengths around 1. m with average power of 30 - 300 mW. The nonlinear optical response of the quantum well SESAM in this regime is investigated using a numerical model in which the resonantly excited carriers are coupled by scattering to states outside the laser bandwidth.