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Solar Laser Pumping, Or Solar Hydrogen (and Magnesium) Part II

Sunlight arrives on earth in almost parallel beams. A mirror reflection of direct sunlight shows you can point it at a distant spot. This ‘quality’ of sunlight is exploited in solar tower power plants. Heliostats all focus the suns reflection on a central reciever where the light is turned into heat (althoug sunlight has a good deal of invisible infra red light to start), and heat into electricity (usually). But sunlight could be more concentrated and thus usefull in different ways if it where used to power lasers. 


Solar laser as a way to create a magnesium economy, maybe a step to far.. (by ELI)

We looked at concentrated sunlight for hydrogen a week ago, and the temperatures for water splittinghave to be high. With solar pumped lasers those temperatures are easy to reach, so this peeked the interest of the japanese researchers. It turns out it is not even that complicated, while the advantages of having your solar energy packaged into a neat beam should be obvious..

Solar concentration fresnel lenses for solar pumped lasers (source)

Looking further into the options I came across an interesting and potentially very usefull line of research, that of solar pumped lasers. This requires some explanation, which is not easy, but bear with us.

Solar pumped laser in action 

Lasers are light sources where the light is traveling in perfect parallele beams. This is why laserlight shone to a far spot makes only a tiny dot. Laser light is produced in crystals that can be exited, so they start to emit light, and that because of their shape and nature will excite light in extremely parralel beams. There are several ways to ‘exite’ laser material, a common way is to shine flash light on it, which is why we associate laser with electrical sparks and high electric buzz. In the research I came across it is suggested it is done using focussed sunlight.

"Solar pumped laser has been studied. Recently, ceramic laser pumped by

pseudo solar light shows high efficiency of 43%." (source)

Solar Pumped Laser

So you can make laser beams with sunlight, and you can do that with reasonable efficiency, meaning (as stated above) 43% of the energy in the sunlight is transferred it laser light. What does this mean?

sunlight continuously exites the laser chrystal that is doped to absorb visible light 

In the article by Kazuo Imasaki et al. it means one can run a chemical process of hydrogen generation more efficiently. This is mainly because the laser can transfer the energy (which turns from light into heat) fast, with low losses and very precise into a reaction container. Imagine you make a heat storage vessel with a tiny hole where the laser comes in, the heat loss from the vessel is extremely low because the ususal pipes and such don’t exist. The laser can transport energy into small well insulated spaces to reach extreme temperatures.

The production of ammonia using the high temperatures achieveable with solar pumped

laser is deemed a great way to create high energy density fuel 

Another possiblility with solar laser light is it’s direct transportation over considerable distances. One can imagine a solar tower near a town beaming it’s energy to a nearby town, or perhaps through a wide diameter glass fiber tube. This might be less lossy and cheaper to realize than either copper/carbon electricity lines or pipes transporting heated oil, sodium or something like that. The laser idea was created for power beaming to satellites, but here we see that there can be a domestic advantage too.. 

Back from space 

The science is growing, but with a focus on space. Why not on earth, after all not all light is absorbed ealily by our atmosphere.. 

"The solar radiation was chopped at a 20% duty cycle to avoid overloading of the cooling system. The peak power output was more than 65 W during the chopper’s open times

(source)

"A ten megawatt solar-pumped continuous liquid laser system for space applications is examined. 

 " a single inflatable mirror of 434 m diameter used in conjunction with a conical secondary concentrator is sufficient "

(source

More about The laser material 

More about Laser driven vehicles

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