| 摘要 |
PURPOSE:To prevent the lowering of the reflectance with the attaching of material particles to an observation window, by providing a metal thin film at a corner of a roughly L-shaped observation light-guide to make material particles approaching the light-guide attach to the thin film. CONSTITUTION:A light guide cylinder 4 for observation is formed in a roughly L shape and a fine hole is provided at the tip located near a plasma emitting body 1 to form a light-guide port 2 while a metal thin film 11 is arranged at a corner of the light-guide cylinder 4 at a specified angle so that light from the guide port 2 will pass through an observation window 5 via a focusing lens 3. With such an arrangement, material particles scattered by the plasma emitting body 1 approach the light-guide cylinder 4 and mostly attach to the thin film 11. On the other hand, the plasma emission light is reflected on the thin film 11 and focused with the lens 3 to be introduced into the atmosphere from the observation window 5. Then, as the thin film 11 is advanced bit by bit with a winding motor 12, the emission light is reflected on a fresh surface without attached material particles, thereby preventing the lowering of the reflectance. |
