A theoretical model for the prolongation of lifetime of a gaseous plasma channel formed by two pulse technique at laser intensities below the tunnel ionization threshold is developed. The first laser pulse ionizes the gas completely on the axis and partially off the axis, causing self-defocusing of the pulse. After the passage of the pulse, the plasma expands radially, creating an atom/ion density profile with a minimum on the axis. Partial recombination also sets in. As the second pulse arrives, after a time delay of less than the recombination time (~ns), the electrons get heated, and the recombination rate is slowed down. The second pulse self focuses, enhancing the heating rate and lengthening the lifetime of the plasma channel.
