Apparatus for detecting optically defects

DETAILED DESCRIPTION The present invention has for its object to provide a novel and useful apparatus for detecting optically defects in objects with a very high accuracy by means of an objective lens which can be designed under a large freedom.
According to the invention, an apparatus for detecting optically defects in objects comprises: means for emitting a laser light flux having a small diameter; an objective lens having a diameter larger than said diameter of laser light flux for focussing it onto an object to be checked and for collecting a light flux directly reflected by the object and a light flux scattered by a defect in the object; first beam splitting means directing the laser light flux emanating from said laser light emitting means toward the objective lens and for directing said directly reflected and scattered light fluxes emanating from the objective lens toward a direction different from a direction to said emitting means; second beam splitting means for splitting the directly reflected and scattered light fluxes emanating from said first beam splitting means from one another; first light detecting means for receiving the directly reflected light flux emanating from said second beam splitting means to derive a first output signal; means for receiving said first output signal to derive a focussing error signal in accordance with a variation in the directly reflected light flux due to a fluctuation in a distance between the objective lens and the object; means for driving the objective lens into an in-focussed position in response to said focussing error signal; second light detecting means for receiving the scattered light flux emanating from said second beam splitting means to derive a second output signal; and means for receiving at least one of said first and second output signals to produce a detection signal representing an existence of the defects in the object.