Cs. Liu et Vk. Tripathi, Laser frequency upshift, self-defocusing, and ring formation in tunnel ionizing gases and plasmas, PHYS PLASMA, 7(11), 2000, pp. 4360-4363
The combined effects of tunnel ionization of gases on laser frequency upshi
ft, defocusing, and ring formation are considered self-consistently. A high
-intensity short pulse laser causes rapid tunnel ionization of a gas. The i
ncreasing plasma density leads to a decreasing refractive index, modulating
the phase of the laser as it propagates and causing frequency upshift and
supercontinuum generation. For laser intensity profile peaking on axis, the
tunnel ionization produces a minimum of refractive index on axis, thus def
ocusing the laser. The defocusing reduces the ionization rate and frequency
upshift. As the laser propagates over a Rayleigh length its trailing porti
on develops a ring shape distribution due to stronger defocusing of rays on
axis than the off-axis rays, as seen in a recent experiment. (C) 2000 Amer
ican Institute of Physics. [S1070-664X(00)02911-6].