The authors achieved 11%–14% slope efficiency of solar-pumped laser by Cr-codoped Nd:yttrium aluminum garnet ceramic and Fresnel lens focusing from natural sunlight. The laser output of 24.4W was achieved with 1.3m2 Fresnel lens. The maximum output for unit area of sunlight was 18.7W∕m2, which is 2.8 times larger than previous results with mirror collector. The utilization of Cr3+ ion enabled efficient absorption and energy transfer to Nd3+ ion of solar spectrum. The fluorescence yield at 1064nm for various pumping wavelengths was measured both for Crcodoped and nondoped laser media, and 1.8 times enhancement of laser output from sunlight is predicted.
The authors propose an energy cycle based on a renewable fuel. Magnesium is chosen as an energy carrier and is combusted with water to retrieve energy using many power devices. MgO, the combustion residue, is reduced back to Mg by laser radiation generated from solar and other renewable energy sources. They have achieved an energy recovery efficiency of 42.5% for converting MgO to magnesium, using a laser. Combined with a demonstrated 38% efficiency for converting an artificial sunlight source (metal halide lamp) into laser output energy indicates that the proposed energy cycle is already in a feasible range for practical use.
The control of the refractive index of laminated coatings consisting of alternating stacks of nanoscale Al2O3 and TiO2 sublayers grown by atomic layer deposition has been achieved. The refractive index of the coating linearly changed from 1.870 to 2.318 as the thickness of the single TiO2 sublayer was varied from 2.0 to 39 Å while that of the single Al2O3 sublayer was kept constant at 5.5 Å. The refractive index could be varied by adjusting only the number of growth cycles of each material. This approach will have potential applications to optical multilayer coatings consisting of well-controlled extremely thin layers.
Remarkable improvements in the lifetime of the Nd upper level and in the effective stimulated emission cross-section of Nd/ Cr:YAG ceramics have been theoretically and experimentally studied. Until recently, it had been thought that the long energy transition time from Cr ions to Nd ions of Nd/Cr:YAG adversely affects laser action, degrading optical-optical conversion efficiency under CW and flash lamp pumping. However, current research showed that high-efficiency energy transition has a positive effect on laser action. The effective lifetime is increased from 0.23 to 1.1 ms and the emission cross-section is effectively increased to three times for that of the conventional Nd:YAG. A small signal gain is significantly improved, and the saturation power density is reduced to 1/10 that of the Nd:YAG for the same pumping power density. A CW laser light generated in a laser diode (LD)-pumped 1064 nm Nd:YAG laser oscillator was amplified, and the measured output power was saturated. The output laser power calculated using theoretical saturation power density was consistent with the experimental results.
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