Energy absorption and propagation in laser-created sparks.

The energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere have been investigated. To create the sparks, 532 nm pulses from a frequency doubled Q-switched Nd : YAG laser are used. We employed 2 ns gated fast photography for studying the time evolution of the kernel at early times. Optical emission spectroscopy is used to infer temperature and density of the sparks. Significant energy absorption by the plasma is observed just above the breakdown threshold. The energy absorption and propagation in the spark indicated that argon plasma is more absorptive than air plasma. The absorption of the spark increases with laser energy, and at higher energies absorption saturation is observed. A spiky behavior is observed in the transmitted temporal profiles of lasers at higher energies and this is explained as due to the formation of a self-regulating regime.