Toward a solar-powered laser

To most people, the phrase “solar energy” conjures up images of photovoltaic panels or solar thermal collectors. But one long-explored application is the solar-pumped laser, which offers the promise of greater efficiencies both in generating coherent radiation and in converting the Sun’s energy into usable forms. Research on such devices dates back 50 years. Solar irradiation can average several hundred watts per square meter at Earth’s surface, yet early prototypes never produced even 0.1 watt per square meter of sunlight-collecting mirror. One path toward higher efficiencies lies in appropriating a wider swath of the solar spectrum. Doping a common laser material, neodymium-doped yttrium aluminum garnet (Nd:YAG), with chromium ions has shown promise. Shermakhamat Payziyev and Khikmat Makhmudov of the Uzbekistan Academy of Sciences now report on a refinement to further improve performance: shifting the spectral-harnessing responsibilities to a separate region that couples to the laser’s active region. In the pair’s...