Knots of Light
Image © Bonn University by permission
Bonn Physicists make super-Photon
- —A novel light source with multiple applications
- Date: 22/11/2010
Physicists at Bonn University have established a completely new light source, called a Bose-Einstein condensate of photons. Until recently, experts had considered this an impossibility. This method is also suitable for the design of innovative laser-like light sources that radiate in the X-ray range. This breakthrough may possibly afford fabrication techniques for more powerful computer chips. The scientists reported their discovery in the November issue of the journal Nature (doi: 10.1038/nature09567).
By cooling, rubidium atoms and concentrating them into a small space, they suddenly become indistinguishable: They behave like a single huge "superparticle". Physicists call this a Bose-Einstein condensate.
For "light particles", the photons would have to actually form the condensate. Unfortunately, this idea fails in one fundamental problem: If one photon is "cooled", it disappears. To cool light and to focus light at the same time seemed impossible, therefore, until a few months ago. However, the Bonn physicists Jan Klare, Julia Schmitt, Dr. Frank, and Professor Dr. Martin Weitz have now succeeded —a minor sensation.
How warm is the light?
If one heats the tungsten filament of an incandescent bulb, it begins to glow - first red, then yellow and finally blue. A "temperature" may be assigned in this way to each color of light: e.g., blue light is hotter than red. Tungsten glows with a different color than iron, for instance. Physicists calibrate the color temperature by an imaginary object model, the so-called black body. If one were to heat up this body to 5,500 degrees, the same color is produced as sunlight at noon. In other words, midday light 5,500 degrees Celsius, or nearly 5,800 Kelvin. (The Kelvin temperature scale has no negative values, but starts at absolute zero temperature of -273 degrees centigrade, so the Kelvin values are always 273 degrees higher than the corresponding C-values).
If a black body is cooled, the light radiated will, at some point, no longer be in the visible range, but rather, emits only invisible infrared photons. At the same time the black body's radiation intensity is decreasing: The amount of photons with decreasing temperature is always lower. This trend makes it very difficult to form a Bose-Einstein condensation from a necessary amount of cooler photons.
The technique used by the team at Bonn University uses two highly reflective, parallel mirrors, reflecting and trapping a light beam reflecting between the mirrors. Between the reflective surfaces, were dissolved dye molecules with which the photons collide regularly. In these collisions, the photons were absorbed into the molecules, then emitted again. "It brought the photons to the temperature of the dye-liquid," explains Professor Weitz. "So it cools to room temperature, promptly."
A condensate of light
The Bonn physicists next increased the number of photons between the mirrors, by stimulating the dye solution with a laser. This allowed them to focus the light particles and sufficiently cool them to the level that the light became a condensed "super-Photon".
This photonic Bose-Einstein condensate is a completely new light source with laser-like properties. This also offers a distinct advantage over lasers, "We can now establish a laser to produce very short wavelength light - in other words such as UV or X-ray light," said Jan Klare, "Using a photonic Bose-Einstein condensate."
This prospect should please especially chip designers: They use laser light to engrave logic circuits in their semiconductor materials. How fine these structures will be limited, among other things, by the light wavelength: Long wavelength lasers are less suitable for fine work that are short wavelength —like trying to sign a letter with a paintbrush.
X-ray radiation is a much shorter wavelength than visible light. X-ray lasers should therefore accommodate, in principle, on the same silicon area significantly more complex circuits. This will enable a new generation of high-performance chips - and more powerful computers for the end user. In other applications such as spectroscopy or photovoltaics, the method could also be useful.
Contact: Prof. Dr. Martin Weitz Prof. Dr. Martin Weitz Institut für Angewandte Physik der Universität Bonn Institute of Applied Physics, University of Bonn Telefon: 0228/73-4837 oder -4836 Phone: 0228/73-4837 or -4836 E-Mail: Martin.Weitz@uni-bonn.de E-mail: Martin.Weitz @ uni-bonn.de Jan Klärs January Klare Telefon: 0228/73-3453 Phone: 0228/73-3453 Institut für Angewandte Physik der Universität Bonn Institute of Applied Physics, University of Bonn E-Mail: firstname.lastname@example.org E-mail: email@example.com
Original article in German
Transliteration at Google translate
Scientists Create Light Knots (holographically, by computer using the mathematics of light)
- Twisted Physics
- By Jeanna Bryner, LiveScience Managing Editor
- 17 January 2010 01:01 pm ET
- Source: http://www.livescience.com/technology/tying-light-knots-100117.html
- “Their results, detailed online Jan. 17 in the journal Nature Physics, are "firsts" for a couple of reasons. While so-called knot theorists have studied mathematical equations similar to dark knots, the new research created these knots with math functions that followed rules of propagating light. In addition, unlike other dark knots created that have been tangled up with other knots, Dennis and his colleagues produced isolated dark knots within the light beam, he said.
- "For me, it shows how physicists can adapt existing pure mathematics, such as knot theory, and find it manifest in physical phenomena," Dennis said. "It also shows how finely we can control the flow and propagation of laser light using holograms. This degree of control is likely to find applications in future laser devices.”