Scanning apparatus with integrated beam separating and beam-splitting element for scanning a magneto-optical record carrier

Claim 1

Apparatus for scanning a radiation-reflecting information plane of a magneto-optical record carrier, said apparatus comprising a radiation source for providing a linearly polarized scanning beam, an objective system for focussing the scanning beam to form a scanning spot in the information plane which produces a reflected beam of radiation therefrom, the reflected beam sharing a portion of the radiation path traversed by said scanning beam between the radiation source and the scanning spot, means arranged in said portion of said radiation path for separating the scanning beam from the reflected beam, and a radiation-sensitive detection system for converting the reflected beam into electrical signals; characterized in that: the beam-separating means is included in a single integrated optical element comprising: a transparent supporting body having first and second substantially parallel planar surfaces, said supporting body being disposed in said portion of said radiation path so that a normal to said surfaces thereof extends at an acute angle to a principal axis of the reflected beam incident thereon; a semi-transparent mirror on a portion of said first surface for separating the scanning beam and the reflected radiation beam, said mirror thereby constituting said beam-separating means; and means for splitting the separated reflected beam by partial transmission and partial reflection or by bi-refringence into two sub-beams which are orthogonally polarized with respect to each other; and further characterized in that the radiation detection system comprises means responsive to said two sub-beams to produce two electric signals respectively corresponding thereto, and means for producing an output electric signal corresponding to the difference between said two signals; said output electric signal being indicative of a direction of polarization rotation of the reflected beam and thereby also being indicative of a magnetization direction of said information plane in the region of said scanning spot.