Focus position changing apparatus and confocal optical apparatus using the same

A confocal optical apparatus comprising:

• a light source;
• an aperture plate in which a plurality of confocal apertures are formed;
• an objective lens configured to converge each of light beams having passed through the plurality of confocal apertures, at an object side converging point, and to again converge each of reflected light beams formed by reflection of converged light beams at a measurement object, at each of the confocal apertures respectively corresponding to object side converging points;
• a focus position changing unit configured to include a plurality of optical path changing pieces which are each formed of a parallel plate-shaped transparent body and which differ from each other at least in one of a refractive index and a thickness, a rotating plate on which the plurality of optical path changing pieces are arranged along a rotation direction of the rotating plate so as to cross an optical axis of the objective lens, the rotating plate having an anti-reflection layer formed in a predetermined region on a first surface of the rotating plate on a side of the light source, and a driving unit configured to rotate the rotating plate, the focus position changing unit being configured to discretely change a focus position of the objective lens in an optical axis direction each time the optical path changing piece crossing the optical axis is changed by rotation of the rotating plate;
• and
• an imaging system configured to receive a light beam that is reflected by the measurement object and again converged at the confocal aperture,
• wherein the rotating plate includes a plurality of light beam passing portions configured to respectively correspond to the plurality of optical path changing pieces,
• wherein each of the plurality of optical path changing pieces is provided at a position which is located on a second surface of the rotating plate opposite to the side of the light source and which corresponds to each of the plurality of light beam passing portions,
• wherein the second surface, on which the plurality of optical path changing pieces is provided, is formed flat such that unintended inclination of the plurality of optical path changing pieces is prevented, and
• wherein the predetermined region is a region on the first surface, and is a region at least including a region to be irradiated with a light beam of the light source except regions the plurality of the light beam passing portions are provided.