Vertical-external-cavity surface-emitting lasers (VECSELs), also called semiconductor disk lasers (SDLs), have developed strongly during the last two decades. Additionally, the range of available wavelengths has been drastically extended during this time, especially when second harmonic generation is taken into account. Nevertheless, these systems run into limits when the refractive indices of the materials used for the necessary distributed Bragg reflectors (DBRs) approach too much. This leads to a much higher number of necessary layer pairs, which increases the structure thickness and makes growth of such DBRs at least extremely difficult. Another limit occurs when the band gap of the gain material used in the VECSEL approaches too close to the band-gap in the used DBR materials. Absorption losses in the DBR are the consequence. Additionally, the performance of VECSELs in general suffers from heat incorporation into the active region caused by the excess energy of the pump photons together with the low thermal conductivity of the substrate and the included DBR.
The recently shown membrane external-cavity surface-emitting laser (MECSEL) concept opens the potential to overcome all the above named challenges as only an isolated active region membrane, sandwiched between intra-cavity heat spreaders is used as gain material. Furthermore, active region membranes in the GaInP/AlGaInP material system aiming on the yellow and red-orange spectral region where direct laser emission has not been realized yet, grown on high-index substrates, open the possibility to deliver sufficient gain realizing a MECSEL.
Hermann Kahle, Kostiantyn Nechay, Jussi-Pekka Penttinen, Jari Lyytikäinen, and Mircea Guina, "Towards direct emitting MECSELs in the yellow and red-orange spectral range (Conference Presentation)," Proc. SPIE 10515, Vertical External Cavity Surface Emitting Lasers (VECSELs) VIII, 1051509 (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290174.5751421402001.
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