| 摘要 |
PURPOSE:To perform accurate measurement of thickness only by measuring the difference in light receiving times, by scanning reflected light beams, which take different light paths in correspondence with the distance between first and second reflecting surfaces. CONSTITUTION:Part of laser light is reflected by the surface of a film 14 and becomes a surface reflected light beam. Other part of the laser light is refracted at the same surface, advanced in the film 14, reflected by the interface between a crown cap 14 and the film 14, advanced to the outside of the film 14 again, and becomes a back surface reflected light beam. A galvanomirror 12 is minutely rotated, and the laser light scans the film 14 as shown by an arrow 30. Accompanied by this scanning, the surface reflected light beam and the back surface reflected light beams from the film 14 scan a slit 18 as shown by an arrow 31. An opening width W is determined so that both reflected light beams are not passed at the same time. Therefore, the two reflected light beams are inputted in a detector 16 at the different times. |
