IT COULD be the world's shortest movie. Two carefully timed
laser pulses have allowed chemists to film a molecule moving
between two states - a process that lasts less than a
picosecond. Richard Mathies and his colleagues at the University
of California, Berkeley, used Raman spectroscopy, which measures
the frequency of light scattered by a molecule, to deduce its
chemical structure. This has allowed them to take femtosecond
(10-15 second) snapshots of the process and string them together
to form a movie. The resolution of each snapshot depends on the
length of the light pulse. Previous attempts at using Raman
spectroscopy to visualise chemical reactions achieved picosecond
(10-12 second) resolution. But the shorter pulses required for
femtosecond images did not produce enough scattered photons to
achieve a useful image. Mathies and his team got round this by
shining a picosecond pulse of light on the molecule to increase
the number ...