Inverse Bremsstrahlung in Weakly Ionized Underdense Plasmas*

Laser-induced air breakdown has attracted much attention in many applications such as laser ignition, laser breakdown spectroscopy. The breakdown and energy transfer are dominated by the properties of a weakly ionized plasma, which is characterized by a collision with the neutral gas. In order to predict threshold conditions of the laser breakdown precisely, it is necessary to understand the details of the laser energy absorption and ionization degree in the weakly ionized plasma. The coefficient of classical absorption were investigated for various degree of ionization.