The pulse of speed

-- (Credit: Shri Krishan)IMAGINE a pulse of light which lasts for
only a few hundred billionths of a billionth of a second (10-18 seconds, or an
attosecond). This is about the time that
light travelling at 300 million metres per
second takes to move across an atom!

If the calculations of some theorists
are correct, it would be possible to generate such a short-lived pulse. Currently the fastest pulse has a duration of about
a ferntosecond, which is 1,000 times
longer than the attosecond pulse.
Shortening of the pulse time is a difficult
task. The pulse has to be composed of
many different frequencies, all of which
need to be coherent or in phase. The
pulse has to be strong enough to be of
use and the consecutive pulses have to
be separated by about a millionth of a
second (Science, Vol 269).

The theoretical ideas of Paul
Corkurn and his colleagues at the
National Research Council at Ottawa,
Canada, have the potential of meeting
these challenges. These researchers plan
to use a pulse from a titanium sapphire
laser to ionize a gas of xenon or argon.
The laser light will generate an oscillazing electric field which will force'the
electrons in the ionized gas to move at
extremely high energies. These electrons
will collide with their parents to generate a high energy photon.

Limiting the number of gas atoms
used and making use of special metallic
filters, Corkurn plans to generate a pulse
of ultraviolet'light lasting only about
400 attdseconds. These short-lived pulses could prove to be a wonderful tool to
study natural phenomenon which occur
at such short time scales. For instance, a
laser firing attosecond pulses could be
used as ,a high speed flash to "see" the
motion.%)f electrons, the formation of
chemical bonds or even the formation
of molecules.

The researchers feel that though no
group has all the equipment required to
generate an attosecond pulse and mea-
sure it, it is only a matter of a couple of
years before it becomes a reality and we
are able to actually see the electrons in
motion around the nucleus.