Number 823, May 8, 2007
by Phil Schewe and Ben Stein
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.
"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