Abstract: Optical record carrier scanning apparatus including a source of radiation which is tunable to produce different wavelengths of a radiation beam and an optical assembly for forming the radiation beam into a spot for scanning information tracks on the record carrier. The optical assembly includes a diffraction grating which diffracts the beam so that only a selected diffraction order sub-beam thereof is formed into the scanning spot, the diffraction angle of such sub-beam and consequently the position of the scanning spot relative to the track being scanned being variable by variation of the wavelength of the radiation beam. A periodic transverse variation of spot position can thus be produced entirely optoelectronically, for producing a tracking error signal to control the scanning spot to remain centered on the information track.

Abstract: An apparatus is described for optically scanning an information surface by moving said surface relative to a beam, which apparatus comprises a radiation source for supplying a beam, a collimator lens and an objective for focusing the beam to a spot in the information plane. The height of the apparatus can be reduced and/or a beam having an asymmetrical cross-section can be converted into a beam having a symmetrical cross-section by arranging a reflective diffraction grating with a suitable grating period between the collimator lens and the objective, while the angle of incidence between the normal on the grating and the chief ray of the scanning beam deviates considerably from 45.degree..