[en] Soft x-ray emission from plasmas produced by ablation from a magnesium target employing a ruby laser is studied using a grazing incidence spectrograph in the spectral region 3-12 nm. Emission intensities are investigated for different ionic lines as a function of position, time after the maximum of the laser pulse and laser irradiance. A gated pinhole camera is employed for studying the evolution of the plasma at early stages. The propagation distances and velocities are measured. Our results show that the line intensities of all ionic lines increase with laser irradiance until a saturation plateau is observed at high irradiance levels. The increase in ionization and intensity saturation with varying laser irradiance seems to suggest strong interaction of the laser pulse with the dense plasma formed near the target within the pulse duration. (author)

[en] The emission features of laser ablated graphite plume generated in a helium ambient atmosphere have been investigated with time and space resolved plasma diagnostic technique. Time resolved optical emission spectroscopy is employed to reveal the velocity distribution of different species ejected during ablation. At lower values of laser fluences only a slowly propagating component of C₂ is seen. At high fluences emission from C₂ shows a twin peak distribution in time. The formation of an emission peak with diminished time delay giving an energetic peak at higher laser fluences is attributed to many body recombination. It is also observed that these double peaks get modified into triple peak time of flight distribution at distances greater than 16 mm from the target. The occurrence of multiple peaks in the C₂ emission is mainly due to the delays caused from the different formation mechanism of C₂ species. The velocity distribution of the faster peak exhibits an oscillating character with distance from the target surface. copyright 1997 American Institute of Physics

[en] Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained. copyright 1997 American Institute of Physics

[en] 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

[en] The dynamics and confinement of laser-created plumes expanding across a transverse magnetic field have been investigated. 1.06 μm, 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