PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 735 June 29, 2005 by Phillip F. Schewe, Ben Stein
SOLITON TRANSISTOR. A transistor based not on the customary
sandwich of semiconductor layers but on a Josephson junction (itself
a sandwich consisting of two superconducting layers separated by a
thin film of insulating material) architecture, and involving not
the gated flow of electrons or holes (the empty spaces left behind
by electrons) but the controllable flow of tiny magnetic vortices,
has been built and tested by Farshid Raissi, a scientist at the
Toosi University of Technology in Tehran. The vortices, set in
motion in the form of solitons (pulses that do not lose energy or
their shape as they travel) travel at the speed of light and
therefore are much faster than the electrons in ordinary
transistors, possibly leading, Raissi argues, to quicker switching
speeds (raissi@xxxxxxxxxx). In his experimental transistor setup,
which is about 800 microns long, trains of vortex solitons, created
by applying small applied magnetic fields to the junction and set in
motion by a applying a brief current into the junction, are used to
control the flow of a separate soliton train. Part of the reason
solitons can be used in this controllable way (and controlling
flow---turning a component on or off---is one of the hallmarks of
transistors) is the fact that solitons can be made to annihilate
with anti-solitons (solitons consisting of vortices established with
a contrary magnetic orientation). With his vortex-soliton
transistor Raissi has observed switching speeds of 8 GHz, as fast or
faster than the best existing transistors. Raissi expects no
insurmountable problems in shrinking and mass producing his soliton
device, and expects to achieve speeds of 200 GHz, which would make
this transistor architecture quite attractive for use in
supercomputers. (Applied Physics Letters, 27 June 2005 lab website,
http://www.ee.kntu.ac.ir )
ULTRAVIOLET FREQUENCY COMB. Physicists at JILA, the joint institute
of NIST and the University of Colorado, have created a new optical
process to extend the production of coherent radiation into the
extreme ultraviolet region of the electromagnetic spectrum. This
process takes advantage of the fact that ultrafast laser pulses of
femtosecond widths, separated by nanoseconds, manifest themselves as
a superposition of light at different frequencies over a wide
spectral band. The Fourier transform of these short pulses is long
series of evenly spaced spikes; that look like the tines of a comb
(for background, see Physics Today, June 2000). What's new is that
the JILA researchers have pushed the coverage of the frequency comb
into the extreme ultraviolet by generating a series of high
harmonics of the original, near-infrared laser frequency comb. (A
comparable result has also been achieved by Ted Hansch's group in
Munich, a result to be published elsewhere.) In the JILA
experiment, 50-femtosecond-long pulses, spaced 10 nanoseconds apart,
are sent into a coherent storage device---an optical buildup cavity.
The cavity length is determined so that each tine of the incoming
frequency comb is matched to a respective cavity resonance mode. In
other words, the pulse train is matched exactly into the cavity such
that a pulse running around inside the cavity is reinforced by a
steady stream of incoming pulses. After a thousand roundtrips
through the cavity, the infrared laser light becomes sufficiently
energized to directly ionize xenon atoms inside the cavity. The
quick repatriation of the xenon electrons to their home atoms is
what produces light pulses of high frequency harmonics. Coherent
high harmonic generation has been achieved with other techniques,
typically involving single, actively amplified, ultrashort laser
pulses. The new approach demonstrated in the JILA work has
drastically improved the spectral resolution of these high harmonic
generated light sources by many orders of magnitude and will also
permit an important increase of the efficiency of the harmonic
generation process. Moreover, the buildup of intense UV happened
without the need for expensive or bulky amplifying equipment.
Optical frequency combs have led to demonstrations of optical atomic
clocks and are furthering research in extreme nonlinear optics,
precision spectroscopy, and laser pulse manipulation and control.
Jun Ye (ye@xxxxxxxxxxxxxxxxx, 303-735-3171) and his colleagues
believe that the new ultraviolet frequency comb promises to provide
an important tool for ultrahigh resolution spectroscopy and
precision measurement in that spectral domain. It will open the door
to unprecedented spectral resolution, making it possible for
scientists to study the fine structure of atoms and molecules with
coherent XUV light. (Jones et al., Physical Review Letters, 20 May
2005, Cover Figure article; http://jilawww.colorado.edu/YeLabs/ )
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PHYSICS NEWS UPDATE is a digest of physics news items arising
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Physics News Update appears approximately once a week.
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Re: FETs Vesus Bipolars, Why More Efficient? ... > physically why a transistor is voltage controlled apart from simply ... > years backwards in Physics.... Applying a voltage to a diode will cause a current through it. ... > A normal transistor is a small device that uses a current to control... (sci.electronics.design)
Re: BJT Can be Considered a CCCS in some situations ... >> People who persist in claiming that a transistor is physically a CCCS ... >> nonsense theoretical nonsense on the physics groups.... The reality is that collector charge motion is not the result of base ... (sci.electronics.design)
Re: BJT Can be Considered a CCCS in some situations ... > John Woodgate wrote: ... People who persist in claiming that a transistor is physically a CCCS ...theoretical nonsense on the physics groups.... (sci.electronics.design)
Re: Magnetic field and relative motion ... Once we have solved the riddles,... > physics is a sham, too, once they solve the riddles. ... > of the transistor and is totally irrelevant to understanding semi- ... > long before the transistor was invented, ... (sci.physics.relativity)
Re: Solitons in One Post [Was: Solitons in one sentence] ... I am by no means an expert on solitons and their applications (just ...>physics in terms of solitons. ... These tend to be in a non-linear manner that leads to a certain ... I also note that EM still remains linear.... (sci.physics.research)
