Schijn een lichtje op mijn ... : Bonn Physicists Create A 'Super-Photon'; Completely New Source Of Light For Many Applications

[Henk Elegeert]

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Wednesday, November 24, 2010
 Bonn Physicists Create A 'Super-Photon'; Completely New Source Of Light For
Many Applications
<http://nanopatentsandinnovations.blogspot.com/2010/11/bonn-physicists-create-super-photon.html>
 Physicists from the University of Bonn have developed a completely new
source of light, a so-called Bose-Einstein condensate consisting of photons.
Until recently, expert had thought this impossible. This method may
potentially be suitable for designing novel light sources resembling lasers
that work in the x-ray range. Among other applications, they might allow
building more powerful computer chips. The scientists are reporting on their
discovery in the upcoming issue of the journal *Nature*.

This is an illustration of the "super-photon."

Credit: (c) Jan Klaers, University of Bonn

By cooling Rubidium atoms deeply and concentrating a sufficient number of
them in a compact space, they suddenly become indistinguishable. They behave
like a single huge "super particle." Physicists call this a Bose-Einstein
condensate.

For "light particles," or photons, this should also work. Unfortunately,
this idea faces a fundamental problem. When photons are "cooled down," they
disappear. Until a few months ago, it seemed impossible to cool light while
concentrating it at the same time. The Bonn physicists Jan Klärs, Julian
Schmitt, Dr. Frank Vewinger, and Professor Dr. Martin Weitz have, however,
succeeded in doing this – a minor sensation.

*How warm is light?*
When the tungsten filament of a light bulb is heated, it starts glowing –
first red, then yellow, and finally bluish. Thus, each color of the light
can be assigned a "formation temperature." Blue light is warmer than red
light, but tungsten glows differently than iron, for example. This is why
physicists calibrate color temperature based on a theoretical model object,
a so-called black body. If this body were heated to a temperature of 5,500
centigrade, it would have about the same color as sunlight at noon. In other
words: noon light has a temperature of 5,500 degrees Celsius or not quite
5,800 Kelvin (the Kelvin scale does not know any negative values; instead,
it starts at absolute zero or -273 centigrade; consequently, Kelvin values
are always 273 degrees higher than the corresponding Celsius values).

When a black body is cooled down, it will at some point radiate no longer in
the visible range; instead, it will only give off invisible infrared
photons. At the same time, its radiation intensity will decrease. The number
of photons becomes smaller as the temperature falls. This is what makes it
so difficult to get the quantity of cool photons that is required for
Bose-Einstein condensation to occur.

And yet, the Bonn researchers succeeded by using two highly reflective
mirrors between which they kept bouncing a light beam back and forth.
Between the reflective surfaces there were dissolved pigment molecules with
which the photons collided periodically. In these collisions, the molecules
'swallowed' the photons and then 'spit' them out again. "During this
process, the photons assumed the temperature of the fluid," explained
Professor Weitz. "They cooled each other off to room temperature this way,
and they did it without getting lost in the process."

The creators of the "super-photon" are Julian Schmitt (left), Jan Klaers,
Dr. Frank Vewinger and professor Dr. Martin Weitz (right).

*Credit:* (c) Volker Lannert / University of Bonn

*A condensate made of light*
The Bonn physicists then increased the quantity of photons between the
mirrors by exciting the pigment solution using a laser. This allowed them to
concentrate the cooled-off light particles so strongly that they condensed
into a "super-photon."

This photonic Bose-Einstein condensate is a completely new source of light
that has characteristics resembling lasers. But compared to lasers, they
have a decisive advantage, "We are currently not capable of producing lasers
that generate very short-wave light – i.e. in the UV or X-ray range,"
explained Jan Klärs. "With a photonic Bose-Einstein condensate this should,
however, be possible."

This prospect should primarily please chip designers. They use laser light
for etching logic circuits into their semiconductor materials. How fine
these structures can be is limited by the wavelength of the light, among
other factors. Long-wavelength lasers are less well suited to precision work
than short-wavelength ones – it is as if you tried to sign a letter with a
paintbrush.

X-ray radiation has a much shorter wavelength than visible light. In
principle, X-ray lasers should thus allow applying much more complex
circuits on the same silicon surface. This would allow creating a new
generation of high-performance chips - and consequently, more powerful
computers for end users. The process could also be useful in other
applications such as spectroscopy or photovoltaics.

Contacts and sources:
Prof. Dr. Martin Weitz  <Martin.Weitz at uni-bonn.de>
Institut für Angewandte Physik der Universität Bonn
Jan Klärs  <%20klaers at iap.uni-bonn.de>
Institut für Angewandte Physik der Universität Bonn

University of Bonn <http://www.uni-bonn.de/>
"

Henk Elegeert

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