Laser plasma formation using dual pulse pre-ionization

This contribution details an experimental and theoretical study of tailoring laser plasma temperature using two overlapped laser pulses of nanosecond duration. The method utilizes an ultraviolet pulsed laser beam to achieve pre-ionization, followed by a second, nearinfrared, superimposed pulse to provide energy addition in a controllable fashion through electron avalanche ionization (EAI). Experiments were conducted in atmospheric pressure air. It was observed during experiments, and through numerical simulations, that the preionization beam influences the breakdown threshold of the overlapped second beam. A subsequent study used laser Schlieren images as a diagnostic tool to aid the understanding of the temporal and spatial evolution of the breakdown kernel. Schlieren images of the overlapped ultraviolet and near-infrared beams were obtained at various time-delays for both breakdown and below breakdown conditions.