Abstract
The recent progress in solar-pumped laser with Fresnel lens and Cr:Nd:YAG ceramic medium has revitalized solar laser researches, revealing a promising future for renewable reduction of magnesium from magnesium oxide. Here we show a big advance in solar laser collection efficiency by utilizing an economical Fresnel lens and a most widely used Nd:YAG single-crystal rod. The incoming solar radiation from the sun is focused by a 0.9 m diameter Fresnel lens. A dielectric totally internally reflecting secondary concentrator is employed to couple the concentrated solar radiation from the focal zone to a 4 mm diameter Nd:YAG rod within a conical pumping cavity. 12.3 W cw laser power is produced, corresponding to 19.3 W/m(2) collection efficiency, which is 2.9 times larger than the previous results with Nd:YAG single-crystal medium. Record-high slope efficiency of 3.9% is also registered. Laser beam quality is considerably improved by pumping a 3 mm diameter Nd:YAG rod.
Highlights
Our planet receives more energy from the Sun in one hour than all humankind consumes in an entire year
The recent progress with Fresnel lens and Cr:Nd:YAG ceramic laser medium has revitalized the solar laser researches by providing 18.7-19.5 W/m2 collection efficiency [8,9,10,11]
For a magnesium combustion engine to function as a practical source of renewable energy, the lasers need to be pumped by solar power
Summary
Our planet receives more energy from the Sun in one hour than all humankind consumes in an entire year. Fresnel lens is cost-effective, but the largely dispersed radiation distributed along its focal zone hampers further efficient light concentration to a thin rod For this reason, a novel secondary laser pumping scheme becomes indispensable. A modified version of the DTIRC with a large curved input face and a small planar output face is utilized by us to concentrate efficiently the solar radiations from the focal zone to the thin rod, which is mounted within the conical pumping cavity. With the 4 mm diameter rod, maximum laser output power is 12.3 W, corresponding to 19.3 W/m2 collection efficiency, which is 2.9 times larger than the previous record of 6.7 W/m2 with a large diameter Nd:YAG rod and a mirror type concentrator [6] This result is, to the best of our knowledge, the highest collection efficiency achieved with Nd:YAG medium. The large increase in slope efficiency and the substantial reduction in threshold pump power are interesting features of our prototype solar laser
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