Fun_People Archive
21 Feb
Physics News Bits - AIPBPN update.415

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From: Peter Langston <psl>
Date: Sun, 21 Feb 99 23:34:51 -0800
To: Fun_People
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Subject: Physics News Bits - AIPBPN update.415

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[Science fiction fans who remember "slow glass" will find the first item a
 bit familiar... -psl]
From: AIP listserver <physnews@aip.org>

Excerpted-from: PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 415 February 18, 1999   by Phillip F. Schewe and Ben
Stein

LIGHT HAS BEEN SLOWED TO A SPEED OF 17 m/sec by passing it through a
Bose-Einstein condensate (BEC) of sodium atoms at nK temperatures.  In
general light is slowed in certain materials, a property exploited in making
optical lenses.  As the index of refraction of these materials gets higher,
however, absorption increasingly takes its toll on the light beam.  In an
experiment at Harvard (Lene Vestergaard Hau, hau@rowland.org), physicists
have used a BEC (and its enormous index of refraction) as the optical
medium, but with the following important modification.  They contrived a
system of laser beams whose pattern of interference created an effect called
electromagnetically induced transparency, allowing light to propagate
unabsorbed but at greatly reduced speeds, in this case a factor of twenty
million compared to the speed of light in vacuum; greater light-speed slow
downs are expected, to as low as cm/sec.  The researchers also observed
unprecedentedly large intensity-dependent light transmission.  Such an
extreme nonlinear effect can perhaps be used in a number of opto-electronic
components (switches, memory, delay lines) and in converting light from one
wavelength to another.  (Hau et al., Nature, 18 February 1999.)

TUNABLE X-RAY WAVEGUIDE WITH AN AIR GAP.  At synchrotron light sources,
electron beams make floods of x rays which must be tamed before they can be
used in experiments where typically they probe the structure of some tiny
biological sample.  One of the ways to focus the beam onto the sample is to
compress it and guide the x rays through a thin strip of material sandwiched
between reflecting surfaces.   Usually the guiding material, often carbon,
absorbs a substantial portion of the x rays.  Researchers at the University
of Amsterdam (Friso van der Veen, vdveen@wins.uva.nl,  011-31-20-525-6330)
have now produced a waveguide out of two parallel reflecting plates with
only air in between.  This not only greatly reduces x ray losses but also,
when the gap is filled with liquid, permits the x-ray study of lubricants
and colloids.  In optics geometry is destiny; the coherent wave pattern in
the Amsterdam device can be tuned by prising apart the two flat plates which
form the body of the waveguide.  For the whole process to work the plates
(only about 250 nm apart) must be extremely parallel, the equivalent of
suspending one soccer field over another at a height of about 5 mm.  (M.J.
Zwanenburg et al., Physical Review Letters, 22 Feb; see figure at
www.aip.org/physnews/graphics.)

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© 1999 Peter Langston