Criss-crossing Laser Beams Zoom Electrons
Crossing two high-intensity laser beams in a plasma (a collection
of charged particles) can have some interesting effects. In a recent
experiment performed by researchers at the University of Michigan and
the Institute of Physics in China, energy from a higher-power laser
pulse was transferred to a lower-power laser pulse. The lower-power
pulse had been accelerating electrons with its "wakefield"
(like a wave accelerating a surfer). The extra energy to this lower-power
pulse enhanced the electron acceleration and decreased the divergence
of the electron beam. These features are desirable for proposed "laser
particle accelerators" that would be powered by relatively inexpensive
and convenient laser light, which is much more powerful than conventional
How does this effect come about? When the laser beams cross at right
angles, an interference pattern forms. In the criss-cross zone (indicated
by the bright light coming from the intersection region of the two beams
in the photo), the interference pattern reflects light in much the same
way as does a mirror, redirecting it perpendicular to its original travel.
The interference also heats electrons.
In addition to enhancing laser accelerators, this optical beamsplitting
effect is expected to play a role in experiments that use lasers to
produce fusion energy. In those experiments, high-power laser beams
cross each other when heating and compressing a capsule of fusion fuel
(for example, solid deuterium). The effects of criss-crossing beams
will unavoidably divert some of the laser energy from its original direction,
and must be taken into account so as to maximize the effectiveness of
using lasers to produce fusion energy.
Thanks to Donald Umstadter, University of Michigan, for the images
and help with the caption.
Reported by: P.
Zhang, N. Saleh, S. Chen, Z. M. Sheng, and D. Umstadter, Physical
Review Letters, 28 November 2003.