Expansion Rates of the Luminous Front of a Laser-Produced Plasma

The expansion velocity of the luminous front of a plasma plume created by a giant pulse laser has been measured both as a function of time during the laser pulse and as a function of position in front of the pyrolitic graphite target. The initial velocity of the vapor appears to agree with the sublimation temperature of pyrolitic graphite. The subsequent vapor absorption of laser radiation produced peak final expansion velocities of 7 × 106 cm/sec. The luminous front was found to accelerate from 4.8 × 105 to 7.0 × 106 cm/sec within a 0.3-cm distance for a laser energy density of 700 J/cm2.