U.S. Hang Gliding Pilots

Metaphorically speaking, however, plasmons seem to have rendered one scientist invisible, at least in terms of broad recognition: Robert W. Wood, a physics professor at Johns Hopkins University who first observed so-called "field emissions" -- charged particles emitted from a conductor in an electric field -- in 1897. (This effect became the basis for field-emission microscopes, used to study atomic structure.) Wood was also the first person to unwittingly record the energy lost as heat by plasmons skimming along the surface of metals in 1902, although he couldn't explain the effect at the time. It took 40 years for Italian physicist Ugo Fano to provide an explanation: metals are not perfect conductors, as had been previously believed. Fano found that a conducting surface could guide light as a 2D surface wave (which is why plasmons are also known as two-dimensional light). Those waves absorb energy, which explains Wood's anomalous observations of energy loss in the light reflected from metallic surfaces.

So technically, Wood "discovered" plasmons; he just didn't realize it. And while he was internationally known at the time for his many achievements in optics and spectroscopy, nowadays, his name is hardly a household word, even within the physics community. He's more of a historical curiosity, a footnote to the many scientific papers now being published on plasmon-related research; Wikipedia only has him listed as a "stub." Personally, I blame those mischievous little plasmons. They have cunningly shielded him from the recognition he so richly deserves. To me, Wood is physics' Invisible Man.

That's a shame, because he certainly had an interesting and varied career. Black lights are sometimes known as "Wood lights" in his honor, since he is considered the father of infrared and ultraviolet photography. Using a glass filter that would transmit only UV light, he photographed the moon, demonstrating that the darkest area in UV light is the Aristarchus Plateau. The Wood crater on the far side of the moon is named after him. He was the first to publish infrared photographs of landscapes in 1910, which were later exhibited at the Royal Photographic Society. And in 1919 he published the first ultraviolet photographs of the human body.

Unlike most modern physicists, Wood's research involved almost no mathematics; he thought math was boring, and preferred to focus on pictures and showy demonstrations during his class lectures, sometimes involving small explosions or flames. He never earned a bona fide PhD, and funded his early post-undergraduate studies by working part-time as a bottle-washer. His well-known fondness for pranks paid off around 1906, when he famously debunked Henri Blondlot's claim to have discovered a new form of invisible radiation, "N-rays." (This was just a few years after Wilhelm Roentgen discovered X-rays, so the public was inclined to be a bit more credulous about the existence of invisible radiation.) Blondlot claimed the N-rays could only be detected with his own machine. Wood secretly removed the inner workings of the machine -- specifically, a prism -- and when Blondlot repeated the demonstration, he still claimed to see his N-rays, unaware his "detector" no longer worked. Wood was highly amused; one assumes Blondlot was not.

As if those accomplishments weren't enough, Wood also invented the method for thawing frozen street water mains by passing an electric current them; the frosted glass bulb; even a method for detecting forged documents that was very cutting edge in his day. He experimented with aerial photography by attaching a camera to a kite. And during a trip to Germany in August 1896, Wood photographed a few test flights by famed aviator Otto Lilienthal -- literally one week before Lilienthal plunged to his death during another test flight when his glider stalled out. He even published a children's book of nonsense verse in 1907, How To Tell the Birds from the Flowers.

Plasmons are back in the science news this year, thanks to several papers presented at the APS March meeting in Baltimore last week on the emerging field of plasmonics. To date, it's proven difficult to combine photonic components -- such as fiber optic cables -- with electronic components like wires and transistors because of their mismatched capabilities and size scales. Photonic components can carry a lot of data -- witness the explosion in broadband data transmission rates -- but are bulkier than electronic components, which in turn can carry less data. The Holy Grail is to be able to combine the best features of both onto a single chip. Plasmons might be the key to achieving it, since they operate at optical frequencies -- typically 100,000 times greater than the frequency of even the most cutting-edge microprocessors -- and the higher the frequency of the wave, the more information you can transport over it. Yet they take up much less space because their wavelengths are much smaller than the light used to create them.

This makes plasmons extremely promising for a wide range of applications -- not just to make things "invisible," but also to enable scientists to see fine details that were previously undetectable. For instance, a team of scientists at the University of Maryland are developing a two-dimensional plasmon microscope, ideal for imaging living cells, that could operate much like a point-and-shoot camera and reveal much more detail that currently available with existing imaging techniques. Other researchers are exploiting plasmons to create "super lenses," relying on tiny nanoparticles to amplify and focus the light shining on a given sample. Scientists at the University of Texas, for example, have built a "super lens" and used it in a device to take pictures just below the surface of thin material substrates. Quote from http://twistedphysics.typepad.com/cockt ... re/page/2/ by Posted by Jennifer Ouellette on December 17, 2007