Laser-based diagnostics for condensation in laser-ablated copper plasmas

The thermodynamic conditions which permit the condensation of laser-ablated copper-plasma plumes are investigated by developing Cu number densities and velocities and Cu2 velocity and temperature data. XeCl excimer laser ablation at 500-100 MW/sq cm produces the copper plasmas which are decelerated and stabilized into clusters by a helium backing gas. Macroscopic particulate result from the clusters in which Cu and Cu2 are examined by means of laser-induced flourescence. A time-of-flight method is used to determine Cu velocities which, at low backing-gas pressure, peak at 2 x 10 to the 6th cm/s. Rotational temperature, vibrational temperature, and the number density of atomic copper are also obtained. At 50 torr, strong Rayleigh scattering from the particulate can be used to measure the particles' location and velocity. The Cu2 particles are formed on a single laser shot since, in the absence of ablation laser pulse, the LIF and Rayleigh-scattered signals disappear. 10 refs