Ultrashort laser pulses have become an indispensable tool
for atomic and molecular research. A new technology makes creating short
infrared pulses easy and cheap.
In a marathon, everyone starts at roughly the same place at
roughly the same time. But the faster runners will gradually increase their
lead, and in the end, the distribution of runners on the street will be very
broad. Something similar happens to a pulse of light sent through a medium. The
pulse is a combination of different colours (or different wavelengths), and
when they are sent through a medium like glass, they travel at slightly
different speeds. This leads to a dispersion effect: the pulse becomes longer
and longer.