PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 823 May 8, 2007 by Phillip F. Schewe, Ben Stein
www.aip.org/pnu
THE SHORTEST LIGHT PULSE EVER
Researchers in Italy have created the shortest light pulse yet-a
single isolated burst of extreme-ultraviolet light that lasts for
only 130 attoseconds (billionths of a billionth of a second).
Shining this ultrashort light pulse on atoms and molecules can
reveal new details of their inner workings--providing benefits to
fundamental science as well as potential industrial applications
such as better controlling chemical reactions. Working at Italy's
National Laboratory for Ultrafast and Ultraintense Optical Science
in Milan (as well as laboratories in Padua and Naples), the
researchers believe that their current technique will allow them to
create even shorter pulses well below 100 attoseconds.
In previous experiments, longer pulses, in the higher hundreds of
attoseconds, have been created. The general process for this
experiment is the same. An intense infrared laser strikes a jet of
gas (usually argon or neon). The laser's powerful electric fields
rock the electrons back and forth, causing them to release a train
of attosecond pulses consisting of high-energy photons (extreme
ultraviolet in this experiment). Creating a single isolated
attosecond pulse, rather than a train of them, is more complex. To
do this, the researchers employ their previously developed technique
for delivering intense short (5 femtosecond) laser pulses to an
argon gas target. They use additional optical techniques (including
the frequency comb that was a subject of the 2005 Nobel Prize in
Physics) for creating and shaping a single attosecond pulse. The
results are being presented this week (paper JThA5) at the
Conference on Lasers and Electro-Optics and the Quantum Electronics
and Laser Science Conference (CLEO/QELS). Expanded story at:
http://www.cleoconference.org/media_center/lightpulse.aspx ; also
see Sansone et al., Science, 20 October 2006.
"HYPERLENS" PROMISES TO SURPASS LIMITS OF ORDINARY MICROSCOPES
A Princeton group led by Evgenii Narimanov will discuss a newly
emerging optical design known as a "far-field hyperlens." The
hyperlens aims to increase light's abilities to image and magnify
submicroscopic objects such as the components of biological cells.
The lens is built with metamaterials, composite objects usually made
from nanometer-scale arrays of rods and ring-shaped structures. It
can project an image relatively far away (therefore making it
"far-field"). The cylindrical shape of the hyperlens can collect
components of the light waves that in a conventional lens would be
lost. This helps the hyperlens capture details smaller than the
wavelength of the illuminating light. In addition to such
"subwavelength imaging," the hyperlens' cylindrical geometry enables
it to magnify an object's image.
The Princeton group theoretically proposed the hyperlens (Jacob,
Alekseyev, Narimanov, Optics Express, Vol. 14, Issue 18, pp.
8247-8256, September 2006), and six months later it was demonstrated
experimentally (see, for example, Science, 315, 1686, 23 March
2007). Nader Engheta's lab at the University of Pennsylvania has
also proposed a device, called a "metamaterial crystal lens,"
essentially equivalent to the hyperlens (Physical Review B 74,
075103, 2006). According to Princeton researcher Zubin Jacob, the
initial prospects for the hyperlens are very promising, for
applications ranging from imaging biological objects to making
nanometer-scale circuit patterns. (Paper QTuD3 at CLEO/QUELS)
MAGNIFYING SUPERLENS RESOLVES DETAILS AS SMALL AS 70 NM
The University of Maryland's Igor Smolyaninov has presented what his
group calls a "magnifying superlens." Initially inspired by John
Pendry's "perfect lens" idea, and drawing upon the Princeton
hyperlens and U-Penn crystal lens concepts as well as Maryland's
previous work, the magnifying superlens uses alternating layers of
negative- and positive-index-of-refraction metamaterials. In
negative-refraction metamaterials, light or other electromagnetic
radiation bends in the opposite direction than it would in ordinary
matter, making it potentially very useful for focusing images. The
new device succeeds in magnifying the object while resolving details
as tiny as 70 nanometers, much smaller than the wavelength of
visible light. (Paper JMA4, CLEO/QELS; also see Smolyaninov et al.,
Science, 315, 1699-1701, 23 March 2007).
OPTOELECTRONIC TWEEZERS PUSH NANOWIRES AROUND
In efforts that can improve studies of biological objects and the
construction of nanotech materials, a Berkeley group has invented
"optoelectronic tweezers," a new way of controlling nanometer-scale
objects. Optoelectronic tweezers, which use optical energy to create
powerful electric forces in carefully prescribed places, differ from
ordinary "optical tweezers," which use optical energy to create
mechanical forces that can push things around. According to
Berkeley's Aaron Ohta, the optoelectronic approach uses much less
power than optical tweezers and the light doesn't need to be as
carefully focused, helping to make the technique potentially easier
for laboratories to implement.
In recent months the Berkeley group has had some success in using
their locally controlled electric fields to manipulate the positions
of tiny nanorods, or nanowires (100 nm in diameter and 1-50 microns
long). Ohta says that the optoelectronic device will possibly be
used to place nanorods for the sake of building 3-D circuitry or for
positioning oblong-shaped cells or cell protrusions with
micron-level precision. (Paper CThGG5; for more information, see
Chiou et al., Nature, 21 July 2005 and
http://www.cleoconference.org/media_center/April27Release.aspx )
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