Ricoh Company, Ltd.

Toshio Kanoh

Junichi Kitabayashi

Taira Kouchiwa

Keishin Tsuchiya

A device for optically measuring an aspheric surface includes a fringe-scanning shearing interferometer for applying a wavefront of illuminating light to the aspheric surface and optically measuring the aspheric surface based on light reflected by the aspheric surface along a measurement optical path. A plurality of ring filters having respective different light-transmitting areas are successively positionable, one at a time, in the illuminating light and outside of the measurement optical path for applying divided portions of the wavefront of illuminating light successively to the aspheric surface. The radius of curvature of the wavefront of illuminating light applied to the aspheric surface is measured.

Device for optically measuring aspheric surface

A method of measuring the origin and amount of a shear between a basic light beam and a reference light beam in a shearing interferometric system. To detect the shear origin, shutters are disposed respectively in the optical paths of the basic and reference light beams. The basic and reference light beams are guided through a condenser lens toward a four-segment light detector. First, the optical path of the reference light beam is closed to allow only the basic light beam to fall on the four-segment light detector. By adjusting the position of the light detector, the position of the basic light beam is identified. Then, the optical path of the basic light beam is closed to allow only the reference light beam to reach the light detector. While output signals from the light detector are being monitored, a shearing member is displaced to shift the reference light beam to detect the shear origin in which the reference and basic light beams are overlapped. To measure the shear amount, light of a plane wave is used as the basic light beam, and the basic and reference light beams caused by an imaging lens to fall on an area sensor are of plane wavefronts. An interference fringe pattern on the area sensor is measured by a fringe scanning process to determine an angle at which the wavefronts of the basic and reference light beams are inclined to each other. The shear amount is computed from the determined angle and the focal length of the imaging lens.

Method of detecting origin of shear and measuring amount of shear in

A fringe scanning shearing interferometer includes a converter lens for converting a wavefront reflected by an object under test illuminated with light into an approximately parallel wavefront, a beam splitter for dividing the approximately parallel wavefront into first and second wavefronts travelling in two directions, a pair of first and second prisms disposed respectively adjacent to the beam splitter in equally spaced relation thereto, a displacement mechanism for displacing the first prism in a direction normal to the direction in which the first wavefront falls on the first prism, a shearing device for slightly displacing the second prism in the same direction as that in which the second wavefront falls on the second prism, a photodetector, and a focusing lens for focusing the first and second wavefronts having passed respectively through the first and second prism, on the photodetector to produce interference fringes thereon.

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Tokyo, Japan

Toshio Kanoh