Eliezer S. Yudkowsky <sentience@pobox.com> Wrote:
>Actual nanotechnology would involve... why, attoseconds,
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 567 November 29, 2001 by Phillip F. Schewe, Ben
Stein, and James Riordon
ATTOSECOND PHYSICS HAS ARRIVED. An Austria-
Canada-Germany collaboration (Ferenc Krausz, Vienna Institute
of Technology, ferenc.krausz@tuwien.ac.at) reports that it has
produced and detected, for the first time, isolated x-ray pulses lasting
on the scale of attoseconds, where one attosecond is a billionth of a
billionth of a second (10^-18 s). The reported pulses, lasting
approximately 650 attoseconds (as) and residing in the soft x-ray
part of the electromagnetic spectrum, subsequently provided
attosecond-scale measurements of a physical phenomenon
(specifically, the detachment of an electron from an atom by an
x-ray photon).
With these observations, and several earlier ones by other
groups, attophysics becomes the short-timescale frontier of
physics. It replaces femtochemistry, the production of light
pulses at the 10^-15 s (femtosecond) scale, in this regard. Just as
a strobelight can yield stop-action photographs of a falling water
drop, femtosecond pulses can capture the ultrafast steps of a
chemical reaction between multiple atoms or molecules. But
attosecond pulses are better equipped to capture the even speedier
motions of electrons within atoms.
If light can be imagined as a wave of peaks and valleys, a one-
second visible light pulse is a train of roughly 600 trillion
(6*10^14) peaks and valleys in length. The researchers report an
attosecond pulse just 200 nanometers long, carrying just over a
dozen peaks and valleys. Therefore, the duration of a light pulse
can be thought of as the length along its direction of travel. A
1.28-second pulse can stretch from an Earthbound laboratory to
the moon; a 650-attosecond pulse would barely span the length of
two typical viruses.
Previous experiments have reported evidence of trains of
attosecond pulses following each other roughly every 1 fs
(Papadogiannis et al, Phys. Rev. Lett., 22 November1999; Paul et
al., Science, 1 June 2001; Bartels et al., Nature, 13 July 2000),
but the new experiment, according to the researchers, represents
the first detection and measurement of isolated attosecond pulses.
Such isolated pulses, Krausz states, are important for taking
attosecond-resolution snapshots of electron motion in atoms.
To accomplish their feat, the researchers first prepared an
intense fsec pulse and aimed it at neon gas. The interaction
between the neon gas and the fsec pulse created an attosecond-
scale pulse in the soft x-ray range. According to a helpful
theoretical picture (Corkum, Physical Review Letters, 27
September 1993), the fsec pulse ejects electrons from neon
atoms, and the resulting oscillations of the electrons in the bath of
fsec light produce an even shorter-duration soft-x-ray pulse.
Producing attosecond light is only half the battle. The
researchers then had to measure its duration. By adjusting the
delay between the times at which the x-ray pulse and a fsec
visible pulse hit a gas of krypton atoms, the researchers affected
the spectrum of energies in the electrons liberated from the
atoms. Such modulations in the observed energy spread served as
evidence for an x-ray pulse of 650 attoseconds. Henry Kapteyn
of JILA/University of Colorado (303-492-819,
kapteyn@jila.colorado.edu), a member of a competing group,
claims that the evidence is ambiguous as to whether the
collaboration detected isolated attosecond pulses or trains of
attosecond pulses. Both Kapteyn and Krausz have respected
colleagues who back their differing views.
However this debate pans out, attosecond metrology has arrived,
and it will doubtlessly lead to some staggering physics
experiments never before possible. (Hentschel et al., Nature, 29
November 2001; some other associated journal articles can be
found at www.aip.org/physnews/select)
John K Clark jonkc@att.net
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