Physicists develop a perfect light trap

Whether in photosynthesis or in a photovoltaic system: if you want to use light efficiently, you have to absorb it as completely as possible. However, this is difficult if the absorption is to take place in a thin layer of material that normally lets a large part of the light pass through.

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Tau.Neutrino said:

Physicists develop a perfect light trap

Whether in photosynthesis or in a photovoltaic system: if you want to use light efficiently, you have to absorb it as completely as possible. However, this is difficult if the absorption is to take place in a thin layer of material that normally lets a large part of the light pass through.

more…

from the article

Now, research teams from TU Wien and from The Hebrew University of Jerusalem have found a surprising trick that allows a beam of light to be completely absorbed even in the thinnest of layers: They built a “light trap” around the thin layer using mirrors and lenses, in which the light beam is steered in a circle and then superimposed on itself—exactly in such a way that the beam of light blocks itself and can no longer leave the system. Thus, the light has no choice but to be absorbed by the thin layer—there is no other way out.

Tau.Neutrino said:

Tau.Neutrino said:

Physicists develop a perfect light trap

Whether in photosynthesis or in a photovoltaic system: if you want to use light efficiently, you have to absorb it as completely as possible. However, this is difficult if the absorption is to take place in a thin layer of material that normally lets a large part of the light pass through.

more…

from the article

Now, research teams from TU Wien and from The Hebrew University of Jerusalem have found a surprising trick that allows a beam of light to be completely absorbed even in the thinnest of layers: They built a “light trap” around the thin layer using mirrors and lenses, in which the light beam is steered in a circle and then superimposed on itself—exactly in such a way that the beam of light blocks itself and can no longer leave the system. Thus, the light has no choice but to be absorbed by the thin layer—there is no other way out.

That sounds good. I wonder if it can be used to trap heat too, rather than just being for PV cells.

party_pants said:

Tau.Neutrino said:

Tau.Neutrino said:

Physicists develop a perfect light trap

Whether in photosynthesis or in a photovoltaic system: if you want to use light efficiently, you have to absorb it as completely as possible. However, this is difficult if the absorption is to take place in a thin layer of material that normally lets a large part of the light pass through.

more…

from the article

Now, research teams from TU Wien and from The Hebrew University of Jerusalem have found a surprising trick that allows a beam of light to be completely absorbed even in the thinnest of layers: They built a “light trap” around the thin layer using mirrors and lenses, in which the light beam is steered in a circle and then superimposed on itself—exactly in such a way that the beam of light blocks itself and can no longer leave the system. Thus, the light has no choice but to be absorbed by the thin layer—there is no other way out.

That sounds good. I wonder if it can be used to trap heat too, rather than just being for PV cells.

“In our approach, we are able to cancel all back-reflections by wave interference”

Nice.

It sounds too good. What about absorption by the mirrors and lenses?

For a single pass through a 1 cm thick glass lens

• 50% loss of UV light.
• 0.8% loss of blue light.
• 0.2% loss of green light.
• 0.1% loss of near infrared light (1 micron).

Loss of light, in reflection from a silver mirror.

• 2% to 14% loss depending on wavelength.

In an aluminium mirror.

• 5% to 13% loss depending on wavelength.

There are special mirrors made from layered dielectrics that have a much lower loss from reflection, but they have to be tuned to a specific wavelength and will absorb light at all other wavelengths.

> What about heat?

Even better for near infrared. (1 micron wavelength).

Not good for thermal infrared (10 micron wavelength) unless you make the mirrors of gold (2.5% loss) and then you lose reflectance in the visible range. Silver mirrors in the thermal infrared range have a 4% loss.

In summary, unless the mirrors are of layered dielectrics tuned to a specific wavelength, 25 passes of light through the thin sample is about the maximum you can expect.