Abstract
Membrane external-cavity surface-emitting lasers (MECSELs) have great potential of power scaling owing to the possibility of double-side cooling and a thinner active structure. Here, we systematically investigate the limits of heat transfer capabilities with various heat spreader and pumping parameters. The thermal simulations employ the finite-element method and are validated with experimental results. The simulations reveal that double-side cooling lowers the temperature by about a factor of two compared to single-side cooling when diamond and silicon carbide (SiC) heat spreaders are used. In comparison, the benefit for a thermally worse conductive heat spreader is larger, i.e. a fourfold decrease for sapphire. Furthermore, we investigate the limits of power scaling imposed by the intrinsic lateral heat flow of the heat spreaders that sets how much the pump beam diameter can be enlarged while having efficient cooling. To this end, the simulations for sapphire reveal a limit for the pump beam diameter within the hundred micrometer range, while for SiC and diamond the limit is more than double. Moreover, pumping with a super-Gaussian beam profile could further reduce the temperature rise near the center of the pump area compared with a Gaussian beam. Finally, we investigate the benefits of double-side pumping of thick membrane gain structures, revealing a more homogeneous axial temperature distribution than for single-side pumping. This can be crucial for gain membranes with thicknesses larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1\,\mu \text{m}$ </tex-math></inline-formula> to fully exploit the power-scaling ability of MECSEL technology.
Highlights
The membrane external-cavity surface-emitting laser (MECSEL) architecture has recently emerged [1]–[3] to further expand the versatility of the larger class of semiconductor disk laser technology [4]–[6]
The improved thermal behavior of MECSELs has been well recognized and analyzed for the case when diamond is used as a heat spreader [2]; this heat spreader approach is widely used for vertical-externalcavity surface-emitting laser (VECSEL) and offers a good reference point to understand the benefits of MECSELs in terms of heat management
Our finite-element thermal model shows that the double-side cooling approach of the MECSEL gain sandwich reduces the temperature rise by a factor of up to two when using silicon carbide (SiC) or diamond heat spreaders
Summary
The membrane external-cavity surface-emitting laser (MECSEL) architecture has recently emerged [1]–[3] to further expand the versatility of the larger class of semiconductor disk laser technology [4]–[6]. The improved thermal behavior of MECSELs has been well recognized and analyzed for the case when diamond is used as a heat spreader [2]; this heat spreader approach is widely used for VECSELs and offers a good reference point to understand the benefits of MECSELs in terms of heat management. As it can be seen, these advantages are remarkable and have pointed out to the possibility of using more affordable heat spreaders with lower thermal conductivity, such as SiC [8], [9], yet enabling power scaling to watt-levels [10], [11]. The temperature rise is simulated for different pump beam diameters having different spatial distributions
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