Greetings.
The incident solar spectrum usually has the highest irradiation in the visible range. However I am interested in using particles, which show high absorptivity in the IR range (>1000nm wavelength) .
I roughly remember reflected solar light is usually long wave IR. I would like to know if the light reflected from a commercial solar reflector material will have the same intensity, and will the reflected wave be longwave in the IR region.
I am interested in determining (theoretical formulations/ using empirical relations) the wavelength of the reflected wave from the reflectors if I have the incident solar spectrum.
Any help will be highly appreciated
Regards
Sai Kiran Hota
https://www.sciencedirect.com/search?qs=wavelength%20of%20incident%20solar%20radiation&show=25&sortBy=relevance
Dear Sai,
If you have an optical reflector, the reflector bounces a part or all the incident radiation. The reflected wave has the same wavelength of the incident radiation. According to the geometrical theory of reflection the angle of incidence is equal to the angle of reflection of the optical rays.
If the material is partly reflecting then part of the refracted rays will be absorbed and the rest will go out of the material, that is transmitted.
The absorption properties of the material is characterized by the absorption coefficient alpha which is a function of the wavelength lambda. Each material has specific absorption efficient curve depending on its energy band structure.
Semiconductors show low pass characteristics where they start absorption at a specific critical wavelength. So, a semiconductor material absorbing near infrared wavelength will absorb also the shorter wavelength.
If a material is heated up by a solar energy it begins to emit black body radiation according to its temperature. This radiation is normally of longer wavelength because of low temperature. This may be the type of radiation which you intend.
These are the major concepts of reflection, refraction and absorption of incident radiation an a solid material. I hope it will benefit you.
Best wishes
Thank you Dr.Akram for the useful reference.
Thank you Dr.Zekry for the answer. So, I am trying to use mirco sized particle which has high extinction coefficient (based on results from Mie-theory/Geometric optics) in the early IR region, and hence the idea of using the reflectors which reflect in long wavelengths of low IR (around 1000nm-2500nm, late solar spectrum).
As you pointed out, a reflector under the sun light, has higher surface temperature than the ambient and hence could reflect in long wavelengths. So I would like to know what theory can be used to calculate the wavelengths based on the surface properties/temperature. (I am not sure if Planck's law holds true here).
Could you kindly provide a little more information from your understanding and possibly references that point towards calculating the reflected wavelength from a reflector, in accordance to your second last paragraph.
One point is to clear when a body absorbs solar radiation it becomes hotter than the environment and accordingly emits relatively long wave radiation according to it temperature. This long wave radiation is an emission radiation not a reflection radiation. Do you agree with me? If you agree with me we can go to the next point of the longwave radiation spectrum i,e, wavelengths.
Please answer me as soon as possible.
Best wishes
Yes Dr.Zekry. It shall be an emission radiation and not a reflection.
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