Science > Physics > PHYSICS NEWS UPDATE -- Number 839 September 17, 2007 by PhillipF. Schewe
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PHYSICS NEWS UPDATE -- Number 839 September 17, 2007 by PhillipF. Schewe |
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 839 September 17, 2007 by Phillip F. Schewe
www.aip.org/pnu
RADIO-COOLED MACROSCOPIC OBJECT. Lasers have long been used to cool
atoms in traps. By using light slightly mistuned with the atom*s
own internal quantum energy levels, the light can progressively slow
the atoms almost to a halt. The same principles can be applied to
larger objects made of trillions of atoms, such as a thin silicon
cantilever. Although light cooling of a cantilever-specifically the
cantilever*s oscillatory motions---has been achieved before,
scientists at the NIST lab in Boulder, Colorado are the first to do
this using very radio-frequency circuitry. In the NIST experiment,
a micron-sized cantilever is chilled from room temperature down to
45 K in a process called capacitive cooling, in which the
cantilever, pelted with radio waves, slows down (vibrates less) by
transferring energy to the surrounding radio frequency resonant
circuit. One of the NIST scientists, Kenton Brown
(krbrown@boulder.nist.gov, 303-497-4364) says that the potential
advantage here is that the cooling of the cantilever can be
accomplished with standard radio-frequency technology instead of
with precision optical elements or lasers, making it easier to put
the whole setup on a chip and to immerse the chip in a cryogenic
environment. Why chill the cantilever (think of a tiny up-and-down
vibrating diving board) in the first place? Because a cold enough
cantilever could demonstrate quantum behavior in a macroscopic
object. Besides the fundamental interest in such a feat, it might
pave the way to very sensitive detectors. (Brown et al., Physical
Review Letters, upcoming article; journalists can obtain the text at
www.aip.org/physnews/select; lab website for NIST Time and Frequency
Division, http://tf.nist.gov/ion/index.htm)
AN ULTRAFAST, ULTRALARGE CHANGE IN REFLECTIVITY can be brought about
with femtosecond lasers. In a recent experiment short laser pulses,
falling on an organic salt target, momentarily changed the material
from an insulator (a bad reflector of light) to a semi-metal (good
reflector of light). The change in reflectivity this large---more
than 100%-has never been achieved before in a photonic material;
photo-induced changes are usually more like a few percent. The
laser pulse required doesn*t even have to be particularly intense to
cause the change. Thus gigantic photo-response work began as a
Tokyo-Kyoto collaboration but now includes also LBL and Oxford. The
new advance is that the change in reflectivity can be brought about
in tens of femtoseconds rather than 150 ns. The new results are
being reported this week at the Frontiers in Optics meeting in San
Jose by Jiro Itatani, who has a joint appointment at LBL
(jitatani@lbl.gov) and the Japan Science and Technology Agency. He
says that dramatic reflectivity changes will be useful in bringing
about direct ultrafast optical-to-optical switching. (Meeting
website: http://www.osa.org/meetings/annual/default.aspx)
EXPLAINING A PLASMON VERSION OF YOUNG*S EXPERIMENT. When light
strikes a metallic array of subwavelength apertures surface plasmons
may be created. An electromagnetic phenomenon like light itself,
the plasmons propagate in the plane of the metal but with a
wavelength smaller, sometimes appreciably smaller, than the
illuminating light. Just as light can couple to surface plasmons,
these plasmons propagating between apertures can also be
reconstituted as light. The overall effect is that *large* light
can pass through tiny holes. If now the number of openings is
limited to two, then one has the makings of a plasmonic version of
the famous Young's experiment, the early nineteenth-century
experiment in which light falling on two slits in a baffle produced
an interference pattern---revealing the wave nature of light. A
number of experiments have now been performed on exactly this
version of Young's experiment. At the Frontiers in Optics meeting
C.H. Gan of the University of North Carolina (Charlotte) reports on
some new theoretical predictions relating to the coherence
properties of light transmitted through the slits. His detailed
simulations, done with collaborators G. Gbur of UNC Charlotte and
T.D. Visser of the Free University of Amsterdam, show how surface
plasmons traveling between the apertures result in a correlation of
the light fields emitted from the apertures. Gan (chgan@uncc.edu)
shows how this effect can be tuned (such as by varying the size or
spacing of the slits) to achieve varying degrees of spatial
coherence (that is, the amount by which the waves are *in step*)
of the emergent reconstituted light waves. This tunability in turn has
the potential to be exploited in new forms of coherence-relating
imaging, such as 'variable coherence scattering microscopy.
***********
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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