We report on an orange-emitting intracavity frequency-doubled semiconductor disk laser based on the material system GaAsSb/GaAs. The infrared fundamental wavelength of λ=1220 nm corresponds to a second-harmonic wavelength of λ=610 nm. The second-harmonic generation is done using a lithium–triborate crystal as the nonlinear material. We have achieved an orange continuous-wave frequency-doubled laser output power of 30 mW in the fundamental transverse mode at a wavelength of λ=610 nm.

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The next generation of multi-junction concentrator solar cells will have to reach higher efficiencies than today's devices. At the same time these solar cells must be reliable in the field, be manufacturable with good yield and at sufficiently low cost. Inevitably the request of higher efficiency requires four or even more junction devices. A four-junction solar cell combination of GaInP/GaAs//GaInAsP/GaInAs with bandgap energies of 1.9, 1.4, 1.1, 0.7 eV is developed in a close collaboration between the Fraunhofer ISE, Soitec, CEA-LETI and HZB. This 4-junction cell hits close to the optimum of theoretical efficiency contour plots and has the potential to reach efficiencies up to 50 % under concentration. Challenges are associated with lattice-mismatch between GaAs and InP which is overcome by direct wafer-bonding. The high cost of the InP is addressed by the use of engineered substrates which only require a 500 nm thin mono-crystalline InP layer instead of several hundr ed m. Excellent solar cell results up to 44.7 % efficiency have been obtained under concentration for devices manufactured on InP bulk substrates. The high cell efficiency is also supported by out-door characterization of one cell below a Fresnel lens with 16 cm2 aperture area. 38.5 % conversion efficiency has been measured for this mono-module in Freiburg under real operating conditions without any corrections

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