Perturbations of conduction in liquids by pulsed laser-generated plasma

The observation of optical perturbations of electrical conduction processes in aqueous solutions by laser-produced plasmas is reported. The irradiation of a liquid in a conduction cell with a pulsed tightly focused Q-switched Nd/sup +3/:YAG laser produces plasma that modifies the conductivity of the medium and generates a voltage pulse that can be recorded at the cathode using the same procedure, as in optogalvanic spectroscopy. At low voltages across the cell, this electrical pulse is a positive voltage change, which returns to the equilibrium potential in times much longer than the laser pulse duration. Increasing the cell voltage, this electrical pulse becomes a damped oscillation. Beyond those values, the pulse inverts its sign at the cathode. Results also show that there is a change in cell conductivity in a long-term regime. An interpretation with a first-order model suggests that this behavior could be explained as an excess of ionization, followed by diffusion controlled by recombination in the bulk of the solution.