Semiconductor membrane external-cavity surface-emitting lasers (MECSELs): Power scaling, thermal management, and wavelength extension

Research on semiconductor disk lasers has been driven by their unique features enabling multi watt output power operation with an excellent beam quality. Wavelength versatility is one further key advantage of this technology and is enabled by band gap engineering of various types of available semiconductor gain materials. The wavelength coverage of semiconductor disk lasers is thus, broad and ranges in the fundamental emission from the red to the near infra red. Further extending the wavelength versatility of semiconductor lasers, this work concentrates on an alternative approach, the membrane external-cavity surface-emitting laser (MECSEL), which is similar to a classical semiconductor disk laser but without a distributed Bragg reflector (DBR) and the substrate. The absence of the DBR offers more flexibility in gain chip fabrication. When it comes to thermal management, the gain region in the form of a membrane is cooled between two intra cavity heat spreaders. This double-side cooling approach is remarkable in thermal management, since the gain membrane can be already cooled with relatively poor but more cost-effective heat spreaders, such as silicon carbide (SiC) or sapphire heat spreaders. To better estimate the heat dissipation capability, thermal simulations that are based on experiments, are presented. Several pumping techniques are applied in various MECSEL gain regions emitting in the near infra red spectral regions for power scaling. These techniques include double-side pumping, pump beam area optimization, and parabolic mirror pumping which are relevant for the heat and charge carrier distribution within the membrane and can be applied to generate high power semiconductor membrane lasers. One part of this work concentrates on the critical 1.5 μm wavelength region, at which the DBR quality is low for monolithic integration. A MECSEL with an InAs/InP quantum dot gain membrane sandwiched between two SiC heat spreaders, provides 320 mW output power and 86 nm tuning range. Compared with previous semiconductor disk lasers with a monolithic DBR in this wavelength region, the thermal resistance of 2.3 KW is more than two orders of magnitude lower.