| 摘要 |
The device has a monitoring unit (4) which includes a compact casing enclosing a video camera (12), a wide beam illumination source (14), a narrow beam illumination source (20) and optical components. An operation and control unit (8) includes an optical connector and an electrical mounted on the casing of the monitoring unit in order to connect it, respectively via a fibre optic cable and an electrical cable to the operation and control unit and a table (5) mounted above the treatment chamber. The operation and control unit moves the monitoring unit horizontally along two axes (x,y) to choose a site and provides accurate positioning so that the two beams reflected by the surface layer follow neighbouring optical paths close to the optical axis of the video camera (12). A Wollaston prism (24) is arranged on the optical path of the narrow light beam to obtain two narrow and coherent polarised light beams (25,26) having different directions and orthogonal polarisations. The prism is arranged so that the narrow light beams reflected by the later pass through it. A polariser (27) is arranged on the optical axis of the prism so that the reflects narrow light beam passes through it after its return travel through the prism. The polariser is mounted so that it can rotate with respect to the prism and a detection cell (28).
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