Characterization of laser produced tetrakis (dimethylamino) ethylene plasma in a high-pressure background gas

We present an interferometric and spectroscopic characterization of ultraviolet (UV) laser photoionization of a low ionization potential organic vapor, tetrakis (dimethylamino) ethylene (TMAE), seeded in high-pressure air component gases. These experiments are performed to explore the feasibility of using an electrodeless UV laser preionization of TMAE to initiate a plasma seeded in atmospheric pressure gases that can later be sustained by radiofrequency (RF) power by inductive wave coupling, thereby reducing the initiation RF power budget. A large volume (500 cc), high-density (∼10¹³cm^-3), electrodeless plasma is created by single-photon, 193 nm excimer laser ionization. 105 GHz millimeter-wave interferometry along with optical spectroscopy is employed to investigate the plasma formation and decay characteristics. The TMAE plasma decay mechanisms including two-body and three-body recombination with and without high pressure gases are examined and the dominant loss processes discussed and evaluated. Both density and optical emission measurements show a delay of 140 ± 10 ns in the peak plasma density and emission indicating that the dominant ionization process is delayed ionization via excitation of super-excited states. The experiment also shows that TMAE remains a viable seed gas for UV ionization in the presence of air for t≤10 min.