The dynamics and confinement of laser-created plumes expanding across a transverse magnetic field have been investigated. 1.06 mm, 8 ns pulses from a neodymium-doped yttrium aluminum garnet laser were used to create an aluminum plasma which was allowed to expand across a 0.64 T magnetic field. Fast photography, emission spectroscopy, and time of flight spectroscopy were used as diagnostic tools. Changes in plume structure and dynamics, enhanced emission and ionization, and velocity enhancement were observed in the presence of the magnetic field. Photographic studies showed that the plume is not fully stopped and diffuses across the field. The temperature of the plume was found to increase due to Joule heating and adiabatic compression. The time of flight studies showed that all of the species are slowed down significantly. A multiple peak temporal distribution was observed for neutral species.

The energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere have been investigated. To create the sparks, 532 nm pulses from a frequency doubled Q-switched Nd: YAG laser are used. We employed 2 ns gated fast photography for studying the time evolution of the kernel at early times. Optical emission spectroscopy is used to infer temperature and density of the sparks. Significant energy absorption by the plasma is observed just above the breakdown threshold. The energy absorption and propagation in the spark indicated that argon plasma is more absorptive than air plasma. The absorption of the spark increases with laser energy, and at higher energies absorption saturation is observed. A spiky behavior is observed in the transmitted temporal profiles of lasers at higher energies and this is explained as due to the formation of a self-regulating regime.

The effect of ambient gas on the expansion dynamics of the plasma generated by laser ablation of an aluminum target has been investigated using frequency doubled radiation from a Q-switched Nd:YAG laser. The diagnostic tools include fast photography of overall visible plume emission using a 2 ns gated intensified charged coupled device and space and time resolved emission spectroscopy using a 50 cm monochromator/spectrograph and photomultiplier tube. The expansion behavior of the plasma was studied with ambient air pressure ranging from 10(-6) to 100 Torr. Free expansion, plume splitting and sharpening, hydrodynamic instability, and stagnation of the plume were observed at different pressure levels. Space and time resolved emission spectroscopic studies showed a twin: peak distribution for Al and Al+ species at farther distances illustrating plume splitting at pressures higher than 100 mTorr. Combining imaging together with time resolved emission diagnostics, a triple structure of the plume was observed. The expansion of the plume front was compared with various expansion models and found to be generally in good agreement. (C) 2003 American Institute of Physics.

The dynamics and confinement of laser generated Carbon plumes expanding across a transverse magnetic field have been investigated. 1.06-mu m, 8-ns pulses from an Nd:YAG laser were used to create a plasma that was allowed to expand across a 0.64-T magnetic field. Fast photography employing an intensified charged-coupled device was used for two-dimensional imaging of the plume. Photographic studies showed the collapse of the ablation plume after the bubble lifetime, and formation of two lobes near the target surface at later times.

The laser propagation and energy absorption of an argon spark induced by a laser at different pressures is investigated. 8 ns pulses from a frequency-doubled Q-switched Nd:YAG laser are used to create the spark. The pressure of the argon is varied from 1 atm to 10 Torr. Significant energy absorption by the plasma is observed at high pressures (>100 Torr) while there is negligible absorption when the pressure is lower than 50 Torr. The plasma kernel showed distinct behavior with respect to laser energy. At a laser energy well above the breakdown threshold, the spark moved only in the backward direction and the forward component was absent indicating the strong absorption of the laser by the spark front. A spiky behavior is observed in the transmitted temporal profiles of the laser at higher energies and at high pressures and can be due to the formation of a self-regulating regime. (C) 2003 American Institute of Physics.