Quantum dot membrane external-cavity surface-emitting laser (MECSEL) at 1.5 µm

Similar to vertical-external-cavity surface-emitting lasers (VECSELs) [1] , MECSELs [2] are high beam quality light sources with typical M 2 values close to an ideal Gaussian beam. The difference is the absence of the mono-lithically integrated distributed Bragg reflector. Because of this, MECSELs have a better wavelength flexibility and the potential to provide a wide spectral coverage, achievable by the existing semiconductor material systems. An additional feature of the MECSEL is the double-side cooling [3] , which allows a more efficient thermal management of the laser active structure by the implementation of two transparent heat spreaders. Since the MECSEL is fully operating in transmission, it is possible to pump the laser active structure optically from both sides. This double-side pump approach as present in solid-state lasers, has been applied to 780 nm emitting MECSELs [4] . Also, lateral power scaling by increasing the pump and cavity mode size has been presented in 825 nm emitting MECSELs [5] . So far, MECSELs have been demonstrated and fully characterized with quantum wells in their active regions [6] - [8] .