Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1991-05-29
1993-07-06
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
359222, 356375, G01N 2186
Patent
active
052256901
ABSTRACT:
A narrow gap or unevenness of a surface of a specimen is measured by utilizing the tunnel effect of a light wave reflected at a boundary plane on the condition of total reflection. A laser beam emitted from a laser source is reflected at a surface of a prism on the condition of total reflection in terms of geometrical optics. If a gap between the surface of the prism and the specimen is about the wavelength of the laser beam, part of the laser beam is transmitted into the specimen, and the intensity of the transmitted beam depends on the gap width. A portion of the laser beam is reflected at the boundary plane back into the prism. Therefore, the gap can be measured by measuring the transmittance of the laser beam and comparing the same with the calculated relation between the transmittance and the gap calculated in advance. In practice, the gap width is determined by measuring intensity of the reflected laser beam in the presence of the gap and comparing it to the intensity of the reflected laser beam in the absence of the gap, i.e, when the specimen surface is more than several wavelengths away from the reflecting surface.
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Hirae Sadao
Kouno Motohiro
Nakatani Ikuyoshi
Sakai Takamasa
Dainippon Screen Mfg. Co,. Ltd.
Nelms David C.
Shami K.
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