A most interesting article about the creation of small laser cavities
in zinc oxides...ties in well with chaos and how order appears out or
apparently random behavior....negentropy from entropy;
http://www.sciencedaily.com/releases/1998/12/981218080222.htm
The powdered zinc oxide layer has a highly disordered structure. The
researchers were able to show that this disorder paradoxically
enhances the lasing effect.
Traditional semiconductor lasers, with well-defined cavities, have
perfectly ordered structures to minimize light scattering. In those
devices, normal light scattering reduces laser output.
"We've shown something that is fundamentally new -- a laser without
mirrors, in a totally disordered medium," said Hui Cao, an assistant
professor of physics and astronomy. She and visiting scholar Yi-Guang
Zhao evaluated the laser properties of the zinc oxide films.
"We're exploiting what had been seen as a drawback," Cao said. "People
have been trying to eliminate scattering, which you always think of as
bad for a laser. But we went to the other extreme.
In a totally disordered medium, scattering is very strong, and it
actually helps lasing because it forms closed-loop paths for the light
and creates feedback. It makes its own laser cavities."
When they pumped the zinc oxide layer with a conventional laser at low
power, Cao and Zhao found that the material gave off light with a
broad band of wavelengths.
But as the pump power was increased, the bands sharpened, and above a
certain threshold, very sharp frequency bands appeared. The narrow
frequency range of those bands and their strong polarization confirmed
that the light was in fact a laser emission.
The researchers were actually able to observe the cavities forming and
lasing in the zinc oxide powder film using a special camera at high
magnification.
Cao said that the random orientation of the self-formed laser cavities
in the film is also an advantage because it makes the laser output
omnidirectional.
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