Abstract: A height meter for measuring the height of a first surface of a transparent object is described, which height meter comprises a radiation source for supplying a converging measuring beam whose chief ray extends at an angle to the normal on the surface, and a radiation-sensitive detection unit for detecting a radiation beam reflected by the surface to be measured. Since a diaphragm is arranged in the path of this beam, it is prevented that radiation reflected by a second surface situated opposite the first surface can reach the detection unit. The height meter is notably suitable for an inspection device for a lithographic mask.

Abstract: A description is given of an optical inspection device for inspecting two oppositely located surfaces (3, 4) of a transparent object (1), for example a lithographic mask. The device is constructed in such a manner that for each inspection beam (a, c) the radiation path to the surface to be inspected (3, 4) is substantially equal to the radiation path from the surface to be inspected to a detector (29, 40), so that these paths comprise the same scanning element (10), preferably a mirror polygon. By virtue thereof, the radiation spots formed on the detectors are stationary and an inspection signal having a good signal-to-noise ratio is obtained.

Abstract: A component-detection device for use in a component-mounting machine is described, which device comprises a foreground illumination system and a camera (30), this illumination system comprising at least an optical guide (40) arranged between the component (10) and the camera, and an associated set of radiation sources (45, 46, 47, 48) irradiating the optical guide. This provides a uniform foreground illumination for the component and a reliable detection of this component.

Abstract: Scanning apparatus for a magneto-optical record carrier includes an integrated beam separating and beam splitting element consisting of a supporting body (30) on the surfaces of which are a semi-transparent mirror (22) and a polarization-sensitive beam-splitting layer (26). The semi-transparent mirror separates the scanning beam from the beam reflected from the record carrier. The beam-splitting layer splits the reflected beam into orthogonally polarized sub-beams (27 and 28) which are incident on respective photodiodes or on different regions of a single multiple photodiode. The supporting body may be of a birefringent material which provides orthogonally polarized beam-splitting, in which case the beam splitting layer may be omitted.

Abstract: An optical scanning device is described which comprises a radiation source (6), an objective system (8) and a diffraction grating (9) which is arranged between the objective system and the radiation source to separate the radiation beam (b') reflected by the information surface (2) to be scanned from the beam (b) emitted by the radiation source and for introducing astigmatism in the reflected beam (b') for the purpose of focus-error detection. In principle, the grating (9) has a constant grating period and is arranged at a small angle (.alpha.) in the beam (b').

Abstract: An opto-electronic focussing-error detection system is described for detecting a deviation between a radiation-reflecting surface and a plane of focussing of an objective system in an optical imaging system. The detection system comprises a beam-splitting element and a radiation-sensitive detection system arranged behind the beam-splitting element and two groups of detectors. The first group is associated with a first sub-beam and the second group with a second sub-beam of two sub-beams formed by the beam-splitting element. The beam-splitting element is a compound wedge comprising two wedge sections having a common base surface and each having an upper surface situated opposite the base surface. The upper surfaces are inclined relative to each other in the plane of the interface between the two wedge sections with that plane extending substantially perpendicularly to the base surface and to the upper surfaces and containing the optical axis of the imaging system.

Abstract: An apparatus as described for reading an optical radiation-reflecting information carrier, which apparatus comprises an opto-electronic focussing error detection system with two focussing detectors. The path of the read beam which has been reflected by the information carrier and which originates from the read spot includes a single radiation-deflecting element, in such a way that the radiation which is incident on this element is deflected towards the focussing detectors.

Abstract: An apparatus is described for reading an optically encoded radiation-reflecting information carrier, using an opto-electronic focussing error detection system. The path of the read beam which is directed towards the information carrier includes a radiation-deflecting element producing a narrow focussing beam that co-operates with two focussing detectors to produce an error signal.

Abstract: An apparatus is described for reading a record carrier on which information is stored in an optically readable reflecting structure. By projecting two radiation spots one before and one behind the plane of the information structure, it is possible to ascertain whether a read beam is properly focussed on the information structure. An optical wedge-field lens combination extends the range of operation of the focus correction device.