Abstract: An optical scanning device which includes a radiation source, a mirror objective an a radiation-sensitive detection system, the mirror objective being a transparent body having a radiation window and a reflector symmetrical therewith on each of two opposed surfaces of such body. First diffraction elements are respectively arranged on the first and second radiation window and the second reflector, whereby radiation directed through the first window is focussed to a scanning spot on an information plane and radiation from such plane after a second passage through the mirror objective includes a number of diffracted beams directed on the radiation detection system. The diffracted beams enable detection of tracking errors and focussing errors of the scanning spot relative to tracks on the information plane.

Abstract: An optical scanning device having a mirror-objective arranged between a radiation source and an object to be scanned, which mirror objective is a radiation-transparent body having a radiation window and concentric reflector on each of two opposite surfaces of such body. By providing at least one of the windows with an aspherical shape, the mirror objective is well corrected for spherical aberrations without imposing stringent requirements on the accuracy of such aspherical shape.

Abstract: An achromatic temperature-independent projection lens system for projecting a magnified image of a scene reproduced by means of a reproduction-tube, onto a projection screen. The lens system comprises two correction groups and one main group which provides substantially the entire power of the lens system. The main group comprises a cemented doublet of a convex-concave lens and a biconvex lens and has two spheric outer surfaces. The correction groups each comprise one lens whose surface which faces the image is aspheric.

Abstract: A scanning device for an optical recording and/or reproducing apparatus comprises a mirror objective in the form of a transparent body one surface of which forms an internally reflecting concave reflector and the opposite surface of which forms an internally reflecting convex reflector. A beam of radiation from a radiation source enters a window in the concave reflector, is divergently reflected by the convex reflector back to the concave reflector, and is consequently reflected thereby through a second window in the transparent body so as to form a scanning spot focussed on an information plane to be scanned by the device. The mirror objective includes a phase grating by which radiation reflected from the information surface is separated from the scanning beam and is directed to a radiation-detection system.

Abstract: A single lens is described for forming of a scanning spot on an information surface of a transparent record-carrier substrate. The lens has one aspherical surface and one spherical or plane surface. The curvatures of the lens surfaces and the thickness of the lens are selected to compensate for aberrations caused by the substrate.

Abstract: A single element lens having two aspherical refractive surfaces comprises a lens substrate and two layers of transparent plastic. Each layer has an aspherical outer profile. The lens substrate is a sphere and can be manufactured simply and cheaply.

Abstract: The disclosed method for writing information in a magneto-optical record carrier employs two light beams each positioned on one of two tracks on the record carrier. In one track information is recorded by one light beam, while simultaneously the other track is erased by the other light beam. This enables real time information recording.

Abstract: A record carrier is described which has an optically readable information structure in which information areas of adjacent information track portions have different phase depths, and an apparatus for reading said record carrier. By a suitable choice of the phase depths and by an electronic phase shift of the signals supplied by the read detectors, cross-talk between adjacent tracks can substantially be eliminated.

Abstract: A record carrier is described having an optically readable information structure comprising trackwise arranged information areas which, in the track direction, alternate with intermediate areas, the information being contained in at least the local length of the information areas, of which information structure the average length of the information areas varies. It is demonstrated that by adapting the track period to the average length of the information areas in the tracks, the cross-talk between the tracks may be reduced without essentially reducing the information density.

Abstract: A record carrier is described which has an optically readable information structure in which information areas of adjacent information track portions have different phase depths, and an apparatus for reading said record carrier. By a suitable choice of the phase depths and by an electronic phase shift of the signals supplied by the read detectors, cross-talk between adjacent tracks can substantially be eliminated.

Abstract: An apparatus is described for point-by-point scanning of an object, which may be a phase object, an amplitude object or a combined amplitude and phase object. The object is scanned with a light, sound, electron or X-ray beam which is converged to a spot on the object. A pair of detectors disposed in the path of the modulated radiation coming from the object convert the variations in the radiation into corresponding electrical signals which are fed to a summing circuit. A variable phase shifter connected between at least one of the detectors and the summing circuit is used to introduce a phase shift in the electrical signal such as to optimize the output signal of the summing circuit for the type of object being scanned.

Abstract: A lens having a spherical surface and an aspherical surface curved relative to each other to minimize coma for a large diffraction-limited field and a large numerical aperture.