CO$_{2}$ Laser enhanced lifetime of femtosecond and nanosecond produced air plasmas

Air produced plasmas generated from a 20 mJ femtosecond pulse at 800 nm and a 5 mJ nanosecond pulse at 532 nm were orthogonally enhanced with a 3 J defocused CO$_{2}$ pulse to study the effect of interpulse delay on plasma lifetime. When interpulse delay was optimized with respect to the CO$_{2}$ pulse, both the femtosecond and nanosecond plasmas exhibited longer lifetimes. The impact of CO$_{2}$ laser pulse energy was explored by maintaining a fixed CO$_{2}$ laser fluence at the interaction point. The femtosecond/CO$_{2}$ combination exhibited the same relationship as with the defocused 3 J pulse with a substantial lengthening of plasma lifetime and luminance. The effect of the enhancing wavelength was studied by replacing the CO$_{2}$ laser with a 1064 nm nanosecond laser pulse to monitor any differences in the laser generated air plasmas. The femtosecond/nanosecond combination exhibited quenching of the generated plasma with almost no change in plasma lifetime. A study of these interactions will broaden the understanding of the role of pulse duration and wavelength when considering the phenomena that occur in laser generated plasmas such as inverse bremsstrahlung processes, multi-photon ionization, and collisional heating.