Time resolved laser induced fluorescence on low pressure argon surfatron discharges

In this contribution we report the application of time resolved laser induced fluorescence (tr-LIF) experiments on low pressure argon surfatron plasmas to obtain insight in the argon excitation kinetics. The surfatron device is a microwave-induced plasma that uses surface waves to generate and maintain the discharge. This type of discharge is widely used in industrial applications such as thin films deposition and surface treatment. As a consequence different theories and models are continuously being developed in order to understand the behavior of these plasmas. An essential part of any grand model is the construction of an excitation-ionization scheme (sometimes called collisional radiative model, CRM) that describes the excitation system of the burning gas or gas mixture. The aim of these tr-LIF measurements on argon is to experimentally measure some of the features of the argon atomic system in order to complement and validate future collisional radiative models. The setup used for the tr-LIF experiments is composed of a tunable dye laser in the wavelength range 440 nm - 460 nm, pumped by a frequency doubled Nd:YAG laser (355 nm). The experiments were carried out on surfatron plasmas in pure argon with pressures in the range 0,6 mbar – 5 mbar and microwave powers in the range of 10 W - 70W. In the first phase of this experimental study we pump highly excited levels of the argon system (5p levels). Studying the time decay of the fluorescence signal for different conditions of pressure and electron density it is possible to obtain information about the radiative and collisional mechanisms that rule the population of these atomic levels, namely the electron-atom collisions as well as the heavy particle quenching. Studying the intensity of the signal gives information about the population of the lower excited state of the pumped transition. It is also possible to check the connection between different excited levels by measuring the influence that the laser perturbation has on different levels close to the one being pumped. In the next phase of this study we will pump with higher wavelengths in order to study the perturbations on lower excited states. In this way we will be able to obtain a more complete picture of the argon excitation scheme.