Number 645 #1, July 9, 2003 by Phil Schewe, James Riordon, and Ben Stein
Ultra-intense Light Filaments
Ultra-intense light filaments have successfully been sent through laboratory
"fog" that approximates atmospheric conditions. This is an
important step which should benefit several laser applications, such
as free-space laser communication, monitoring of pollution, and range
finding (see figure).
Open-air laser light shows feature bright beams seemingly traveling
interminably through the sky. But in general water droplets are an avid
absorber of laser light. Now a group of physicists at the Universite
Claude Bernard Lyon in France have used ultra intense (1014
watts/cm2), ultrashort (120 femtosecond) laser pulses to
create "light filaments," streaks of light only 150 microns
wide but hundreds of meters long, which can propagate through an artificial
cloud of water droplets without losing much energy. The filaments form
up through two competing nonlinear optical effects: the "Kerr effect"
in which high intensity light modifies the index of refraction in the
transmission medium (in this case air and water vapor) in such a way
as to cause self-focusing; and the creation of a defocusing plasma effect.
The French researchers now plan to test their scheme in the open atmosphere
under controlled conditions. (Courvoisier
et al., Applied Physics Letters, 14 July 2003; contact
Jean-Pierre Wolf, 04072-43-13-01)