Optical gain achieved in Nd-doped alumina

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, the team experimented with processing techniques. The optimum grain Optical gain achieved in Nd-doped size and concentration resulted when a alumina pressurized mixture of alumina and neoare-earth aluminas have excellent dymium powders was rapidly heated at a thermomechanical properties for highrate of 300°C per minute up to a temperaenergy laser applications, but it has been ture of 1260°C, held at that temperature challenging to create these bulk ceramics for five minutes, and then rapidly cooled with high optical performance. Using a at the same rate. The high temperature innanoscale-focused processing strategy, creased the solubility of neodymium ions University of California, San Diego (UCwhile the rapid cooling rate froze them in San Diego) researchers have now sucplace, Garay says. The rapid heating rate ceeded in observing optical gain in rarekept the grain size to a minimum. earth-doped polycrystalline alumina. As After characterizing their Nd:Al2O3 reported in a recent issue of Light: Science samples using x-ray diffraction measure& Applications (doi:10.1038/s41377-018ments, electron microscopy, and optical 0023-z), the material has thermal conducspectroscopy to confirm the atomic structivity superior to existing solid-state laser ture and the presence of optically active gain media and suggests a path toward neodymium ions in the material, the rebroadening the palette of gain materials. search team optically pumped the material “One of the main problems with solidwith infrared light (806 nm). In response, state lasers is thermal management,” acNd:Al2O3 emitted amplified light at 1064 cording to Javier Garay, the senior scientist nm, revealing net positive gain. behind this research. When pumped, gain The new material displays thermal materials produce heat that degrades the shock resistance that is 24 times that of the beam quality and, in extreme cases, the commonly used gain medium Nd:YAG, as crystal can crack. “If we can improve the well as a broader photoluminescent range thermal conductivity of the gain material, that suggests tunability. Furthermore, then we can really get more power out for Garay says, the result is extendable to other the same cooling and pumping configurasystems. This is not just the development tion,” Garay says. of one new material per se, he says, but a Polycrystalline alumina (Al2O3) has demonstration of the fundamental physics high thermal-shock resistance and fracbehind leveraging length scales to design ture strength, but there are two significant a more diverse group of optical materials. obstacles to its use as a gain medium. Turning the material into a working Unlike yttrium aluminum garnet (YAG, laser is likely to be a significant engiY3Al5O12) and other cubic gain materials, neering and materials challenge. “It was Al2O3 has a hexagonal crystal structure. proved in the 1990s that cubic-type ceramics would be a promising laser material, but today there are only a few researchers who can fabricate high-quality maa b terials,” cautions Akio Ikesue, an expert in ceramic