# Create a laser from sun light

I have read on wikipedia the basic theory behind laser. A photon passes through an excited electron which then produces the exact same photon. Light is bounced off mirrors to create more photons.

Is it possible to make sunlight passes through an optical amplifier to create a amplified sun light stream ?

Ideally the solution could be use with a simple machine that produces laser but instead takes external light as an input. The application would be to put sunlight into an optical fiber and amplify the number of photons using the technique above.

• Just like any other amplifier, a laser can't create more output power than it receives from its power source. I don't know if concentrated sunlight has enough power density to get some laser materials above the laser threshold. I kind of doubt it. Having said that, nothing stops us from converting sunlight into electricity and use that to drive a laser of arbitrary power. – CuriousOne Apr 22 '16 at 8:20
• @CuriousOne The sun does not provide the power but provides the light. Also the concentrated output does not have to be a laser. If just more light comes out of it, it's enough. – Sylvain Apr 22 '16 at 8:42
• For what it's worth, there are naturally-occuring masars (so, microwaves, not visible light), which are presumably driven by sunlight. See here and Wikipedia. This is not quite the same thing that you are talking about, perhaps. – tfb Apr 22 '16 at 9:03
• @tfb not really, I updated my question to provide more background. – Sylvain Apr 22 '16 at 9:06
• You want the amplifier output to have the same spectrum as the incoming sunlight? This is unlikely since most (all known?) optical amplifiers operate on a much narrower band than the black-body-like spectrum of sunlight. – The Photon Apr 22 '16 at 15:10

An inverted laser medium can be used to amplify light in general so in principle this is perfectly possible. The output would however inherit the properties of the sun light and you would not get a laser like type of radiation. What you also have to keep in mind is the limited gain bandwidth of typical laser materials. Ti:sapphire is an example of a very broadband laser medium and still has only $\sim 200\text{ nm}$ gain bandwidth around a center wavelength of $800 \text{ nm}$. Sunlight on the other hand spans the entire visible spectrum. In the figure you can see the actual solar spectrum on the surface and a toy gain profile roughly similar to that of Ti:sapphire

The laser medium will only amplify a certain wavelength range of the sun light so the amplfied sun light would basically mimic the gain profile of the laser medium. The output would just be an spatially and temporally incoherent reddish beam. In the second figure you can see the solar spectrum after amplification with the toy gain profile for various thicknesses of the laser medium.

In my answer I have assumed that you are asking about amplifying sun light with an inverted medium, which is pumped externally. Dirk Bruere's answer and the comments have assumed that you want to invert the medium with sun light.

• I think this is the answer I was looking for, although I am not sure what you mean by "inverted medium". – Sylvain Apr 22 '16 at 18:02
• I am referring to Population inversion i.e. a sufficiently pumped laser medium. – Jannick Apr 22 '16 at 19:39

Sun pumped laser

The two most studied lasing media for solar-pumped lasers have been iodine,1 with a laser wavelength of 1.31 micrometers, and NdCrYAG, which lases at 1.06 micrometers wavelength... The largest solar-pumped laser is currently being operated by a research facility in Uzbekistan. It is a 1 MW solar input power NdYAG type laser, operating at 3,000 degrees C. It is cooled by distilled water.

NdCrYAG is a Neodymium Chromium Yttrium Aluminium Garnet crystal. Iodine, is elemental Iodine. It is not a simple DIY project. More here and Another link

• I have seen this wikipedia page but I don't understand it. What is the lasing media ? What is ionide, NdCrYAG ? Ideally my solution could be DIY made. – Sylvain Apr 22 '16 at 9:04
• @DirkBruere why don't you use the links in the comments for your answer. comments have a way of disappearing here. – anna v Apr 22 '16 at 9:34
• 1 MW solar input power - so that's at least a 1000 sq m collecting area (33m x 33m) - and the link does not say what the output power is. – hdhondt Apr 22 '16 at 10:21

In principle there is nothing wrong with your idea. But I think it is not viable by DIY, at least not with the results I guess you'd be expecting, with such a small understanding of the subject (read: Wikipedia is definitely not enough, and if you were to do things seriously the Sun would be the last source you'd be thinking of). First of all, any lasing medium (the object which contains the excited electrons) only amplifies light in a restricted bandwidth, which means that nearly all the power of sunlight would be wasted. There is no such thing as a "simple machine that produces laser", each laser is built to lase light around a narrow range of wavelenghts. Second of all, in order to DIY an efficient laser without using any pre-built component (which here is the case, as I guess there are no pre-built components for "efficient" solar lasers), you need to know the physics and mathematics behind the lasing mechanism, which includes a basic knowledge on the interaction between radiation and light, some more advanced knowledge on the dynamics of the electromagnetic field both in vacuum and in media, and an actual knowledge of how the theory applies to lasers. Last but not least, with no pre-built components you must be able to do some precision measurements. For example, the laser's resonant cavity (roughly speaking, the apparatus that hosts the mirrors) must be finely tuned in order to be able to amplify the signal.

If you are still determined to build the laser I advise you to get a copy of Svelto's "Principles of Lasers" and/or Saleh's "Fundamentals of Photonics". Here theory is explained in some detail, together with applications to specific laser designs.