Experiments were performed on laser produced plasma from aluminum target discs in a vacuum chamber at pressures a few times 10(-6) torr. Plasma analysis was achieved using a floating double electrostatic probe of tungsten wires biased at -15 volts DC. In analyzing 376 oscilloscope trace pictures of the probe signal, four velocity signals occurred with regularity. The plasma velocities detected by the probe were determined to be 3.7 X 10(7) cm/sec, 1.5 X 10(7)CM/Sec, 5.6 X 10(6) cm/sec (the bulk of the plasma) and 4.o X 10(6) cm/sec. A fifth, very fast signal at 1,0 X 10(6)cm/sec was also detected but it was not consistently present. Investigation of the velocity distributions as a function of time showed them not to be Boltzmann distributions, but exponential power distributions. Investigation of the crater formed by each laser pulse resulted in the determination of the following crater dimensions: crater depth 0.01 cm/shot, crater diameter of 0.11cm and a total spot size diameter of 0.70 cm for the laser-target interaction.
http://archive.org/details/laserplasmaparti00call
Lieutenant, United States Navy
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