Missing order defect detection apparatus

Details Missing order defect detection apparatus Missing order defect detection apparatus

1980-05-30

1982-10-05

Arnold, Bruce Y.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

250550, 250572, 356237, G01N 2132

Patent

active

043525644

ABSTRACT:
A defect detection apparatus is disclosed for optically inspecting a spiral groove of a video disc record by directing a coherent light beam at the grooved surface of the disc. The incident beam illuminates the grooved surface with a light spot that spans a plurality of groove convolutions. The structure of the illuminated region on the grooved surface serves as a diffraction grating for diffracting the incident beam into discrete diffraction orders. Relative motion is established between the disc surface and the incident beam in a manner causing the illuminating spot to rapidly scan the grooved surface in a coarse spiral pattern. A lens system is positioned to collect the light from a single beam of a particular group of non-zero diffraction order beams and to focus this non-zero order beam onto a photodetector. When a defect in the groove pattern exists in the illuminated region the measured power of the non-zero order beam will fall below its normal level. The fractional decrease in the measured power is an indication of the relative size of the defect.

REFERENCES:
patent: 3842194 (1974-10-01), Clemens
patent: 4030835 (1977-06-01), Firester et al.
patent: 4044379 (1977-08-01), Halter
patent: 4069484 (1978-01-01), Firester et al.
patent: 4155098 (1979-05-01), Roach et al.
patent: 4180830 (1979-12-01), Roach
patent: 4197011 (1980-04-01), Hudson

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