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Question:
Solar-pumped laser medium contains various rare metals such as
Chromium, Neodymium, Yttrium.
Struggles for these rare metals become fierce wordwide. Are there sufficient resources for laser medium?

Answer:
The YAG laser medium of 1kW output is expected to be 1cm diameter and 10cm length. Since the specific weight of YAG is 4.5, each laser is only 35g. YAG is composed of Y₃Al₅O₁₂ and hence Yittrium is 45% in weight. Therefore required Yittrium for 1kW laser is only 16g.
As our book “Magnesim Bunmeiron (Magnesium Civilization)” describes, we need to construct 2000 plants of 1000MW laser and hence total Yittrium used for all the plants will be 30,000 tons. Since the estimated resources of Yittrium is 540,000 tons, it is within a reach (Wikipedia describes reserves estimated of Yttrium oxide as 9 million tonnes). Furthermore we can revive the laser media again by baking after it is used for a long time because laser is produced by baking the material. This recycle will be a future subject.
As for the other materials, Nd is 1% and Cr is 0.3 % at most in the laser media. Therefore required amount of Nd and Cr is 300 tons and 90 tons, respectively. This will not cause any problem of resorce shortage.
The advantage of the laser method is that the sunlight is focused into
a small media and thus the required amount of laser media is very small.
(YABE Takashi)

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