We demonstrated a solar-pumped laser with a heliostat–parabolic mirror system. A designed conical pump cavity with a water-filled quartz tube lens was used to couple efficiently the concentrated solar radiation from the focal zone of the primary concentrator into a 5.5-mm-diameter, 95-mm-length grooved Nd:YAG crystal rod within a gold-plated conical pump cavity. For 1.0-m2 effective solar radiation collection area, 20.1-W continuous-wave (CW) output laser power was obtained, corresponding to a total system slope efficiency of 5.04%. This value was 1.31 times higher than the previous with the same solar facility. For 1.5-m2 effective collection area, 34.6-W CW output laser power was achieved at the total system slope efficiency of 4.51%. A strong dependency of laser power on laser rod mounting position was also found.
Solar Pumped Solid State Lasers (SPSSL) is a kind of solid state lasers that can transform solar light into laser directly, with the advantages of least energy transform procedure, higher energy transform efficiency, simpler structure, higher reliability, and longer lifetime, which is suitable for use in unmanned space system, for solar light is the only form of energy source in space.
In order to increase the output power and improve the efficiency of SPSSL, we conducted intensive studies on the suitable laser material selection for solar pump, high efficiency/large aperture focusing optical system, the optimization of concave cavity as the second focusing system, laser material bonding and surface processing. Using bonded and grooved Nd:YAG rod as laser material, large aperture Fresnel lens as the first stage focusing element, concave cavity as the second stage focusing element, we finally got 32.1W/m2 collection efficiency, which is the highest collection efficiency in the world up to now.
The increase of the numbers of laser channel is beneficial to the improvement of laser communication capacity, and a three-longitudinal-mode Nd:YAG laser with a central wavelength of 1.06 μm is studied. The three-longitudinal-mode continuous-wave(CW) laser output is obtained in 808nm LD-pumped 2.4mm Nd: YAG thin disk with a slope efficiency of 11.65% at 20°, the output power of the CW laser is 11.9mW when the power of the pumping is 365mW, and the frequency spacing is 35.4GHz.The maximum output power of 60.3mW is obtained under the 801mW pumped power. The longitudinal mode gain competition is verified in the experiment and the three-longitudinal-mode laser can maintain a stable output when the pumped power reaches 667mW. With the pump power increases, the frequency of laser output power increases, also accompanied by the phenomenon of frequency drift.
This paper designed a circle-shaped Fresnel lens with large aperture as part of the solar pumped laser design project. The Fresnel lens designed in this paper simulate in size 1000mm×1000mm, focus length 1200mm and polymethyl methacrylate (PMMA) material in order to conduct high convergence efficiency. In the light of design requirement of concentric ring with same width of 0.3mm, this paper proposed an optimized Fresnel lens design based on previous sphere design and conduct light tracing simulation in Matlab. This paper also analyzed the effect of light spot size, light intensity distribution, optical efficiency under four conditions, monochromatic parallel light, parallel spectrum light, divergent monochromatic light and sunlight. Design by 550nm wavelength and under the condition of Fresnel reflection, the results indicated that the designed lens could convergent sunlight in diffraction limit of 11.8mm with a 78.7% optical efficiency, better than the sphere cutting design results of 30.4%.
Wireless laser power supply to long-distance devices is drawing more and more interest in recent years. As power receivers, laser cells are adhered on these devices. Relatively high laser cell efficiency could be obtained under a monochromatic illumination. In order to study the most efficient laser illumination conditions to the laser cell, the efficiencies of circular and rectangular cells illuminated by laser with fundamental mode are compared. The simulations show that the cell efficiency increases slowly with the increase of the laser power, and decreases with the increase of the spot size. When the rectangular cell and the circular cell have the same area, and the diameter of the circular cell and that of the laser spot are equal, the efficiency of the circular cell is higher than the rectangular cell.