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by Staff Writers
Vienna, Austria (SPX) Jul 12, 2013
Objects that are smaller than the wavelength of thermal radiation cannot radiate heat efficiently. A generalized theory of thermal radiation has now been experimentally confirmed at the level of a single object at the Vienna University of Technology. All the objects around us emit thermal radiation.
Usually, this radiation can be described very accurately using Planck's law. If, however, the radiating object is smaller than the thermal wavelength, it behaves according to different rules and cannot emit the energy efficiently. This has now been confirmed by a team of researchers at the Vienna University of Technology. These findings are important for heat management of nano-devices and also for the science of aerosols - microparticles suspended in air, which influence the climate.
But while his theory can be applied to many different systems, Planck himself already knew that it is bound to fail and has to be replaced by a more general theory when very small objects are involved.
This has now been investigated at the Vienna University of Technology by Christian Wuttke and Arno Rauschenbeutel (Vienna Center for Quantum Science and Technology, Institute for Atomic and Subatomic Physics, Vienna University of Technology) by studying the heat radiation of ultra-thin optical fibers.
Absorbing and Emitting Radiation
"However, things change if the object is smaller than the typical length over which the radiation is absorbed", says Arno Rauschenbeutel. "In that case, the body cannot fully absorb the incoming radiation, part of it can pass through." As a result, the thermal radiation of the body is altered and does not obey Planck's law any more.
"We could show that the fibers take much longer to reach their equilibrium temperature than a simple application of Planck's law would suggest", says Arno Rauschenbeutel. "However, our findings are in perfect agreement with the more general theory of fluctuational electrodynamics, which allows one to take the geometry and the size of the body into account."
Data Transfer and Soot Particles
More general theories of heat radiation beyond Planck's equations also play an important role in aerosol physics, which deals with tiny particles in the atmosphere. "The thermal radiation of a lump of coal can be described perfectly well by Planck's law, but the behavior of soot particles in the atmosphere can only be described with a more general theory, which we could now further confirm in our experiment", says Arno Rauschenbeutel.
The results of the research project have now been published in the scientific journal "Physical Review Letters".
Vienna University of Technology.
Understanding Time and Space
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