Measurement of dynamics of plasma excited species on dielectric surface using waveguide type optical near field

在最近的放电应用中，等离子体中产生的激发态与介质表面之间的相互作用是非常重要的。发展了一种利用波导型光学近场激光光谱对等离子体介质表面激发态进行定量观测的新技术。1.采用离子交换法在LiNbO_3晶体上制作光波导。用H_3PO_4溶液在高温下进行离子交换，并在氧气中进行退火热处理，以降低传输损耗。通过与波导理论分析的比较，确定最佳波导深度为1.8TMm，激光传输模式为μ。2.利用LiNbO_3和波导，在真空室中搭建了平行板阻挡放电装置。放电是用纯Ar气体产生的。激光从耦合Prizm入射到光波导上，光近场出现在光波导上，与表面附近的Ar亚稳态原子相互作用。在波导中传输后，检测到被吸收的激光。由于光学系统的改进，获得了高S/n3的亚稳吸收信号。从吸收信号中测量了介质表面Ar亚稳态密度随Ar气压高达50Torr的变化，很明显，它与体等离子体中亚稳态密度的关系有很大的不同。实验上发现了一种新的现象，即在放电开始后，透射光强度呈指数级下降。应该对这一现象进行分析。这种实验技术必须与交叉束型光谱方法相结合，才能观察到激发态物种在表面上的动态行为。

In recent discharge applications, an interaction between excited species produced in plasma and dielectric surface is fundamentally important. A new technique using an waveguide type optical near field laser spectroscopy is developed to quantitatively observe the excited species on the dielectric surface in plasma.1.An optical waveguide on LiNbO_3 crystal was produced by ion-exchanging method. Ion-exchange was performed with H_3PO_4 liquid in high temperature and an annealing in oxygen gas made it possible to reduce a transmission loss. From the comparison with theoretical analysis of waveguide, the optimum waveguide depth was determined to be 1.8 μm and the laser transmission in TM0 mode was suit for this experiment2.Using LiNbO_3 with waveguide, a parallel plate barrier discharge device was constructed in a vacuum chamber. The discharge was produced with a pure Ar gas. Laser was incident to the waveguide from a coupling prizm and the optical near field appeared on the waveguide interacted with Ar metastable atoms in the vicinity of surface. After transmitting in the waveguide, the absorbed laser was detected. As a result of improvement of the optical system, the absorption signal due to metastables was obtained with a high S/N.3.Ar metastable density on the dielectric surface was measured from the absorption signal as a function of Ar gas pressure up to 50 Torr and it was clear that the dependence on pressure was much different from the dependence of metastables in bulk plasma. The flux of metastables on the surface was estimated.4.A new phenomenon such that the transmitted laser intensity considerably decreased in exponentially just after the discharge started was found experimentally. This phenomenon should be analyzed. This experimental technique must be mixed with a cross-beam type spectroscopic method in order to observe a dynamic behavior of excited species on the surface.