Abstract: In a signal detecting system in an optical information reading apparatus wherein, in order that a tracking signal having few errors can be obtained, the pupil of an objective used to project a light from a light source as a spot onto the information recording track of a disk, collect the light reflected on the disk and lead it to a light receiving device is covered in the form of a band or a cover plate placed in front of detectors of the light receiving device to intercept a part of the light entering the dectector.

Abstract: In a method and apparatus for detecting an information signal and a focussing error signal of an objective lens with respect to a video disc on which main and sub beams emitted from a laser light source are to be focussed as light spots by the objective lens, the main and sub beams reflected by the video disc are made incident as parallel light fluxes upon a detection prism surface which is set substantially at a critical angle with respect to the main beam, but at an angle smaller or larger than the critical angle with respect to the sub beam, and two light fluxes of the reflected main beam which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the main beam reflected by the reflection surface and perpendicular to the plane of incidence.

Abstract: In a method and apparatus of recording optically an information signal on a disc along tracks by projecting a main beam modulated with the information signal onto the rotating disc by means of an objective lens, in order to obtain focussing and tracking error signals, a sub beam inclined with respect to the main beam is also projected onto the disc by means of the objective lens.

Abstract: A method and apparatus for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens. A light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to peripheral light fluxes reflected by the video disc, and the peripheral light fluxes reflected by the reflection surface are separately received by two light receiving regions which are spaced apart from each other. The focussing error signal is derived as a difference between output signals from the two light receiving regions.

Abstract: Unreacted monomer or monomers and any other volatile organic compounds contained in an aqueous dispersion of polymerizate are removed or separated by a method comprising circulating the aqueous polymerizate dispersion from the bottom of its container to the upper part of the container located over the surface of the dispersion via an exterior conduit. The pressure in the container is maintained at a level reduced to about the saturated vapor pressure of water at the temperature of the dispersion. This manner of separation of monomer from polymer serves to improve the working environment as well as the resulting polymer quality, and the monomer or monomers thus recoverd can be advantageously recycled.