THE EFFECTS OF THE ELECTRIC-FIELD ASSOCIATED WITH A LASER-INDUCED PULSED DISCHARGE ON THE ABLATION-GENERATED PLUMES OF YBA2CU3O7-X

The effects of a pulsed discharge on the luminous plume generated during the excimer laser ablation of YBa2Cu3O7-X are investigated in an oxygen environment. A high-voltage capacitor discharge circuit is used to generate a pulsed discharge. The pulsed discharge is initiated by the laser-induced plume. The electric fields are applied along the trajectory of the plume. The time evolution of the discharge current exhibits a distinct dependence on the polarity and magnitude of the electric field and the oxygen background pressure. When an electric field is applied parallel to the plume trajectory two successive plumes may be observed. The first plume, directly induced by the impact of the ablation pulse upon the target, emits bright light, but is electrically neutral. The second plume (reentrant plume), accompanied by a discharge current (charged plume) is observed a few to 100-mu-s after the first electrically neutral plume. When the parallel field contains a large radial component, i.e., a perpendicular component to the plume trajectory, the charge neutrality of the first plume is lost and only a single charged plume is observed. When the direction of E is reversed (antiparallel field), only a single charged plume is observed directly induced by the laser ablation. The peak current that accompanies the charged plume exceeds 10 A. The time lag of the charged plumes and the minimum voltage required for the discharge are studied as a function of the ambient oxygen pressure. Time-resolved spectra of the plumes are investigated by using a gated intensified diode-array spectrometer. Two-dimensional images of the evolving plume are taken every 100 ns, using a gated, intensified charge-coupled-device camera. A simple model for the observed plume phenomena is proposed.