2-µm high-brilliance micro-cavity VECSEL with >2W output power

This paper presents recent advances of 2-µm GaSb-based vertical external cavity surface emitting laser (VECSEL) with special emphasis on quantum deficit reduction and miniaturization. Operating the VECSEL in a 5-cm long cavity, we could demonstrate an increase in maximum cw output power from 4.2 W to 7.2 W at room temperature when barrier pumping a 2.0-µm emitting VECSEL at a pump wavelength of 1.5 µm instead of 980 nm. Furthermore, miniaturized VECSELs were realized by depositing a high-reflectivity (~97 %) coating on top of a 375-µm thick SiC heat spreader, which acts as output coupler of the micro cavity (µC) formed. This planar cavity is rendered stable by thermal lensing induced by the absorption of pump light. At the same time, thermal lensing influences the beam quality. We will report a detailed study of the influence of the thermal lens on the stability and beam diameter of the µC-VECSEL by using two different VECSEL structures optimized for 980 nm and 1.5 µm barrier pumping, respectively. Using different pump photon energies results in different amounts of heat generated at a given pump photon flux, and thus thermal lenses with different focal lengths. Using the low-quantum deficit pumping scheme we could achieve a factor-7 increase in output power in TEM(00) emission from the µC-VECSEL compared to the 980 nm pumped device, as well as a maximum output power of 2.2 W. This 2-µm µC-VECSEL exhibits 110-nm tunable single-frequency emission at a 7-MHz linewidth at an output power of up to 90 mW. The linewidth of the µC-VECSEL is comparable to that of VCSELs, which typically emit output powers in the milli-Watt range.