On Mar 1, 7:52 pm, (Henry Spencer) wrote:
In article om,

Robert Clark wrote:
"The yet unproven conclusion is that techniques can be developed that will
improve antenna and telescopes resolution that is better than the
diffraction limit."
If this succeeds then telescope apertures will only need to be a
fraction of their current size to achieve the same resolution.

Careful here. "Better than" doesn't necessarily mean "much better than".
If memory serves, the far-field diffraction limit is a fairly direct
consequence of the Uncertainty Principle, which means that you may be able
to cheat on it a bit with a sharp lawyer :-), but it's *not* going to just
go away. Mumbling about "recreating" the evanescent fields ignores the
question of whether enough information is present to do so.

Also note carefully that some of the techniques they are discussing assume
that the shape or some other characteristic of the emitter is *known*.
It's easy to get "resolution" better than the diffraction limit if you
know what you're looking for; for example, a small object can be detected
against a contrasty background even if its size is well below the
diffraction limit. (The classic example is that under good conditions,
astronauts looking down from orbit can see things like roads, which are
demonstrably much narrower than the diffraction limit of their eyes.)

Even the claim that negative-refractive-index microscopy may revolutionize
biology has more hype than substance. There are *already* several methods
for doing *near-field* optical imaging to resolutions much better than the
diffraction limit, and they have proven useful but not revolutionary.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

The Zhang group was able to resolve objects at 1/6th the wavelength,
60 nm as opposed to a 365 nm wavelength. If used with uv light at 200
nm, the lowest wavelength commonly used by biologists in light
microscopy, they could image down to 30 nm. This very likely could
resolve the nanobacteria in real time in "live" conditions.
There are some methods coming into use now that use the near field
light waves to image below the diffraction limit but these are
expensive systems not commonly available to biologists in general:

Near-field Scanning Optical Microscopy.
http://physics.nist.gov/Divisions/Di...nsom/nsom.html

The advantage of these new "near field" lenses is that they will be
much cheaper so every biologists could have one in their tool kit.
Then the existence and prevalence of the nanobacteria will be as
easily determined as microbial cells are now.
It might be though you won't have to create specifically negative
refractive index materials. Here's a another report that easily
creates the same effect:

Phys. Rev. Lett. 94, 057401
(issue of 11 February 2005)
A Microscope from Flatland
"Biologists dream of a point-and-shoot camera that can reveal details
smaller than a wavelength of light in living cells. Now, in the 11
February issue of PRL, researchers show that "two-dimensional" light--
short-wavelength light waves that live on a surface--can improve
resolution without the expensive equipment and special preparations
needed for electron microscopes and other technologies. The team
imaged nanoscale holes as a demonstration, but they believe the
technique could ultimately take instant shots and even movies of the
biological nanoworld."
http://focus.aps.org/story/v15/st3

Note this is still using the near field waves to create this effect.

That negative refractive index materials can be used for the lens far
from the object as in astronomy is indeed not proven but apparently
the Zhang team believes this is possible:

New superlens opens door to nanoscale optical imaging and high-density
optoelectronic devices.
By Sarah Yang, Media Relations | 21 April 2005
http://www.berkeley.edu/news/media/r...uperlens.shtml

The near field effects are purely classical EM effects so are not
dependent on QM for their derivation. It may be that QM will put some
ultimate limitation on how far the subwavelength resolution can go.
Still 1/6th wavelength resolution is still an important advance.


Bob Clark