Electric field strength in a Xe-Ne glow discharge

Many applications of plasma physics are related to light generation. The applications range from TL-tubes until the latest flat displays. The size of discharges is decreasing further and further. At this moment the typical dimensions of a plasma display panel cell are in the order of 100 µm. A model has been developed in the plasma group at Eindhoven to describe these microdischarges [1]. To verify and further improve the model experimental data is needed. Therefore diagnostic tools for this kind of discharge are developed. A laser absorption technique has already been developed by Tachibana et. al. [2]. The diagnostic gives a good insight of the temporal and spatial evolution of metastable xenon in this kind of microdischarge. The diagnostic discussed in this paper tries to use these metastables to measure the electric field. In figure 1 the scheme is depicted. In this scheme the two metastable levels, two resonant levels and the emission dip spectroscopy (e-dip) scheme is illustrated. The e-dip spectroscopy is based on the scheme used e.g. by Döbele et. al. [3] to measure electric field strengths in hydrogen and helium discharges. Xenon is a rare atom and has a closed shell structure in the ground state described in Russell-Saunders notation as 1S0. Exciting one electron out of this structure will leave an inner ion core. This core can have two possible configurations according to Russell-Saunders coupling, 2P3/2 or the 2P1/2 configuration. Racah notation is used to describe the excited levels. 6s[3/2]2 says that the outer electron is excited to the 6s shell. There is no prime so the inner core has 2P3/2 configuration. The angular momentum of the outer electron is coupled with the total angular momentum of the core resulting in 3/2 + 0 = 3/2. The total angular momentum is now 3/2 + 1/2 (spin) = 2. The transition from 6p[3/2]2 to 6s[3/2]2 at 823.2 nm is one of the strongest lines in the xenon spectrum. In this diagnostic we will excite some of the population of the 6p[3/2]2 level to a rydberg state. This will result in dips in the 823.2 line. This e-dip spectroscopy is based on the known stark spectrum as function of electric field strength. To study the feasibility a dielectric barrier discharge is used and a very good spatial resolution is not needed. The first part of this paper the experimental set-up will be discussed. Limits of this method and development in the near future are discussed in the second part.