PURPOSE: To make it possible to inspect even a surface through which a test specimen can be seen with a visual field of the light receiving part restricted by providing a path of reflected beams internally with a photoisolating cutoff member which cuts off reflected beams from an interface other than the surface of the test specimen and a direct light cutoff member which cuts off direct reflected beams from the surface of the test specimen.
CONSTITUTION: A part of an incident beam 7 is reflected on the surface 1 of a test specimen 2 as reflected beams 9, 10 and the remaining penetrates the test specimen 2 by refractive index of the test specimen to be turned into a refracted beam 11. The reflected beams 9, 10 consist of a direct reflected beam 9 reflected on the surface 1 and a scattered beam 10 of the incident beam 7 scattered by surface contamination (stain, etc.). The refracted beam 11 is reflected on the interface of a foreign matter 3 to be an internal reflected beam 12, resulting in separation into reflected beams 9, 10. Path of the reflected beam 12 is provided with a photoisolating cutoff member 15 which cuts off the reflected beam 12 to restrict a visual field estimated by the light receiving part, so that only the reflected beams 9, 10 are received by a photoelectric converter 17. Further, the center of the visual field estimated by the convertor 17 in the path of reflected beams 9, 10 is provided with a direct light cutoff member 14 which cuts off the reflected beam 9 to improve detection precision.
KATO TORU
KOIZUMI MITSUYOSHI
AIKO KENJI
SUZUKI NOBUO
HITACHI ELECTR ENG