PHYSICS NEWS UPDATE -- Number 830 June 27, 2007 by Phillip F. Schewe,Ben Stein

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Date:	27 Jun 2007 11:14:47 AM
Object:	PHYSICS NEWS UPDATE -- Number 830 June 27, 2007 by Phillip F. Schewe,Ben Stein

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 830 June 27, 2007 by Phillip F. Schewe, Ben Stein
www.aip.org/pnu
ALL-OPTICAL MAGNETIC RECORDING has been demonstrated by scientists at
the Radboud University Nijmegen in the Netherlands. Instead of using
the customary magnetic read head to flip the magnetic orientation of a
tiny domain they use the fields present in a short burst of circularly
polarized light. Why use light instead of a magnet? Because the
magnet is relatively slow and because the magnetic field in the light
pulse is intrinsically strong-up to 5 Tesla. The pulses are
perpendicularly incident on the storage medium and the helicity of the
light pulse (whether the polarization is rotating left-handedly or
right-handedly relative to the pulse*s forward direction) establishes
whether the orientation set in the domain will be up or down, or
digital terms, a 1 or a 0. The orientation of the domain (writing a
bit) is accomplished partly through the light*s magnetism and partly
through the localized heating by the pulse, which enhances the domain*s
magnetic susceptibility. The bit can be reversed with light of the
opposite polarization. The light pulse is so carefully focused that it
addresses only one domain at a time (see figure at
http://www.aip.org/png/2007/281.htm).
The speed of the writing process is set by the duration of the laser
pulse, 40 fsec, upsetting certain suggestions, made not so many years
ago, that the speed of recording in optical medium could not shrink
below a picosecond. True, the size of the domain is 5 microns, which
is rather large. However, one of the researchers, Daniel Stanciu
(s.stanciu@science.ru.nl, 31-24-365-3094), says he expects the domain
size to get down to about 100 nm. He believes that the all-optical
approach will eventually be the way of achieving the fastest writing of
data in a magnetic medium. (Stanciu et al., Physical Review Letters,
upcoming article)
A HIGHLY EFFICIENT ROOM-TEMPERATURE NANOLASER has been demonstrated by
scientists at the Yokohama National University in Japan. Made of a
semiconductor material known as gallium indium arsenide phosphate
(GaInAsP), the overall device has a width of several microns
(millionths of a meter), while the part of the device where laser light
actually gets produced has dimensions at the nanometer scale in all
directions. The nanolaser produces steady continuous streams of
near-infrared light and uses only a microwatt of power, one of the
smallest operating powers ever achieved. The design should be useful
in future miniaturized circuits containing optical devices. The laser's
small size and efficiency were made possible by employing a design,
first demonstrated at the California Institute of Technology in 1999,
known as a photonic-crystal laser. In this design, researchers drill a
repeating pattern of holes through the laser material. This pattern is
called a "photonic crystal." The researchers deliberately introduced
an irregularity, or "defect," into the crystal pattern, for example by
slightly shifting the positions of two holes. Together, the photonic
crystal pattern and the defect prevent light waves of most colors
(frequencies) from existing in the structure, with the exception of a
small band of frequencies that can exist in the region near the defect.
By operating at room temperature and in a mode where well-defined laser
light is emitted stably and continuously, the new nanolaser from
Yokohama National University distinguishes itself from previous
designs. According to Yokohama researcher Toshihiko Baba
(baba@ynu.ac.jp), the new nanolaser can be operated in two modes
depending what kind of "Q" value is chosen. Q refers to quality
factor, the ability for an oscillating system to continue before
running out of energy.
Nanolasers operated in a high-Q mode (20,000) will be useful for
optical devices in tiny chips (optical integrated circuits). In a
moderate-Q (1500) configuration the nanolaser requires an extremely
small amount of external power to bring the device to the threshold of
producing laser light. In this near-thresholdless operation, the same
technology will permit the emission of very low light levels, even
single photons. (Nozaki et al., Optics Express, 11 June 2007 issue,
full text available at
http://www.opticsexpress.org/abstract.cfm?id=138211; picture and
extended writeup at
http://osa.org/news/pressroom/release/06.2007/Nanolaser.aspx)
***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
.

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