Apparatus for optically scanning an information plane wherein a diffraction grating splits the beam into two sub-beams

摘要

An apparatus is described for optically scanning an information surface (2). The apparatus comprises a radiation source (4), an objective system (6) and, arranged between them, a diffraction grating (9) for separating the beam reflected by the information surface from the beam (5) emitted by the source and for splitting the reflected beam into two sub- beams (5a, 5b). For each sub-beam there is provided an associated detector pair (16, 17; 18, 19). The grating (9) comprises two sub- gratings (11 and 12) whose grating lines (13, 14) are disposed at opposite angles to the bounding line (26) of the sub-gratings.